This is all of Jack's relationships from throughout the series.
Family
Jack and Castiel
A resurrected Castiel hugs Jack
Jack had chosen his uncle Castiel, since the time he was in his mother's womb, to be his protector. He favored the angel over Dagon and used the promise of a utopia as a means to convince the angel to stay by his mother's side. Castiel dutifully took care of Kelly, ignoring Sam and Dean completely either because he genuinely felt attached to his new ward.
By the time Jack was born, Castiel had been killed by Jack's biological father Lucifer. Jack recalled very little of his time in the womb and claimed that it was his mother who told him that Castiel was the father and that Castiel would keep Jack safe. Jack spent his first few hours alive looking for Castiel as a result. Sam eventually told him that Castiel was gone.
Jack returned to his mother's cabin and witnessed a hunter's funeral being performed on his mother and "father".
Jack soon learns that Dean's dislike in him comes mostly from the fact that Jack caused Castiel's death. When Sam and Dean argue over their opinion of Jack, Jack sadly calls to Castiel and in doing so awakens Castiel in The Empty.
In Tombstone, a resurrected Castiel meets Jack who is shocked to see him alive. He also learns that he played a partial role in bringing him back since it was his pleading that awoke him. Jack hugs Castiel, extremely happy to finally meet him and shows what he has learned from his time with the Winchesters. While working on an assignment, Jack and Castiel catch up with Castiel apologizing for not being there when he needed him but the latter assured him it was alright as he understood it wasn't by choice.
During War of the Worlds, Castiel searched for Jack even seeking aid from the angels. When the angels propose Castiel helped locate Jack and help him rebuild their numbers, Castiel immediately refused as he didn't want to enslave Jack to that pain. Castiel also refused to let Lucifer (who returned from the other world) near Jack even after hearing that Michael (Apocalypse World) intends to invade.
In The Bad Place, Jack states that he sees Castiel and the Winchesters as his family instead of Lucifer.
In Devil's Bargain, Castiel brought up his promise to Kelly Kline that he'd protect her son. To that end, Castiel was ready to go back to the Apocalypse World and save Jack from Michael (Apocalypse World).
Jack and Dean Winchester
Jack and Dean
Dean views Jack as a dangerous being and blames him for the loss of Castiel, as Jack had been the one to convince Castiel to watch over his pregnant mother and leave Sam and Dean behind. Dean spent the months leading up to Jack's birth feeling upset and angry and viewed Castiel's running away with Kelly as the angel being manipulated.
When Jack was finally born, Dean's first response was to shoot him, only for Jack to unleash his powers in self-defense and knock Sam and Dean out. Dean's opinion on Jack didn't improve as he began hunting for the Nephilim. His distrust in Jack contrasts Sam's softer opinion, likely due to Dean's grief caused by losing Castiel again.
Dean does however, give Jack's mother a hunter's funeral alongside Castiel.
Jack soon learns that Dean still doesn't like him and makes a clear effort to emulate Dean in order to appear more likable. Dean is both annoyed and distrustful of Jack. Dean eventually admits to Jack that should Jack go dark side as Dean anticipates, he'll kill Jack himself.[1] Jack overhears an argument between Dean and Sam in which he learns of Dean's negative feeling stem from him blaming Jack for the death of Castiel. In turn, Jack sometimes believes he is evil because of Dean's words, but Sam does his best to cheer Jack up.[2]
| “ | He manipulated him. He made him promises, said paradise on Earth, and Cass bought it and you know what it got him? It got him dead. Now you may be able to forget about that, but I can't! | ” |
— Dean Winchester's initial opinion on Jack
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Jack continues to long for Dean's approval while Dean chooses not to baby him and make him do some of the work during cases, or in Sam's words, treat him like an intern. When Jack becomes dismayed by the lack of approval from the elder Winchester and keeps thinking about Dean's promise to kill him, Sam informs Jack that he can earn Dean's approval through effort, something Dean respects.
While confronting the shapeshifter Buddy, Dean and Jack are both chained up though Dean orders Jack to use his powers to free them. Jack, afraid his lack of control over his own powers may hurt Dean, refuses to obey the order. Jack instead uses his powers to prevent Buddy from shooting at Sam, which gives Sam the opportunity to shoot Buddy, thus solving the case they were working on.
Afterwards, Dean praises Jack for his efforts and acknowledges that he finally did good as Jack smiled to himself at this praise.
With Castiel's resurrection and return, it appeared Dean gave up some of his disdain for Jack since he had partial role in it and he listed Jack as a member of the team. Dean even counted him as a member of Team Free Will and humored Jack on a hunter case but was ready to go along with as it allowed him to act like a cowboy. He was also surprised that Jack was right about it being a case though the monster was something else. Jack wanted to be useful and tried to help Dean by using his powers though unintentionally killed an innocent. Rather than scold Jack, Dean instead told Sam and Castiel to take him back to the Bunker while he deals with the threat. After completing the case, Dean even covered for Jack by putting the innocent's death on the monster. Jack was shown not to accept this and broke down that he might actually be evil but Dean said he wasn't as he admitted that he was wrong in thinking he was.
| “ | I was scared, I was upset, but why would I look for him? He's no one to me. You, Castiel, you're my family.
Yes, we are. |
” |
— Jack and Dean Winchester
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After learning that Jack apparently killed Derek Swan, Dean discussed killing him for it with Sam. However, Dean admitted that he actually liked Jack and saw it as a worst-case scenario that he must be killed. Once they found him, they confronted Jack over his action but he was revealed to be innocent and told them his true intention were to find their mother, which he was able to do letting them know their mother is still alive. When Jack called the Winchesters and Castiel his family, Dean instantly agreed that Jack was family. Dean then praised Jack's initiative in trying to rescue Mary as the latter smiled at his words. Dean continued to be this way when Jack refused to join the angels and wanted to stay with them instead.
During Devil's Bargain, Dean and Sam are told by Castiel that Michael is the that world and he intends to invade. Dean realized Jack and his mother are in danger and they decide to capture Lucifer and open a rift to enter the Apocalypse World to save the pair.
Jack and Kelly Kline
Jack's mother.
Kelly had wanted to start her own family for some time and viewed President Jefferson Rooney, her lover, as the perfect man to be the father. Unfortunately for her, Jeff had been possessed by Lucifer and when Kelly conceived, it was Lucifer's child in her womb. Kelly was told of this by Sam and Dean, but the knowledge did not make her despise the child growing inside her, as she was still the child's mother. She evaded the Winchesters in hopes of keeping the baby safe.
When angels began attacking her, Kelly decided to rely on Dagon as a protector to ensure her baby's survival. She also learned from Dagon that the baby was a boy. Kelly was always concerned for her son's well being and could become frantic when things didn't feel right, such as the "weird little pains" she began experiencing a few months into her pregnancy. When she demanded to have her son looked at, Dagon took her to a clinic where Kelly was able to see her son on a monitor.
This would be the only time mother and son would see each other, as Kelly came to learn from Dagon that birthing half-angels was always fatal to the mothers. This piece of information deeply upset Kelly, and as Dagon's treatment of her worsened, Kelly came to doubt her son's future and felt he might be born as a bringer of destruction. She tried to commit suicide to prevent this possible scenario, but her son responded by resurrecting her and letting her know that he was not evil.
Kelly's love for her son returned, so much that she came to believe her son could save the world. She was able to convince Castiel of these beliefs. When her son began sending her visions from the womb, Kelly chose to trust her son and allowed him to guide her. She accepted Castiel as her son's new protector in place of Dagon. At her new home, Kelly decided to name her son "Jack" and left him a video telling him how much she loved him.
| “ | "I love you." | ” |
— Kelly's last words
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Kelly's belief that the world was dangerous and Castiel would be the one to protect Jack drove the newborn baby to grow into adulthood and seek out his father, whom he thought was Castiel, not Lucifer. After realizing Castiel was dead, Jack returned to Kelly's cabin and mourned her death, showing grief for her. As Sam and Dean prepared a funeral for Kelly and Castiel, Jack was at a loss of words for what to say. Kelly's own last words to Jack were, "I love you".
As Jack struggled to control his powers and dealt with Dean's rejection of him, he came to doubt his own purpose and saw that he might be truly evil. Sam reassured him that he and Kelly believed there was hope for him. Sam later revealed the existence of Kelly's video made for Jack on the day Jack was born. Jack watched it with a sad expression on his face.[3]
Jack speaking with "Kelly"
When Sam and Dean took Jack to a grief counselor as part of a case, Jack decided to ask the grief counselor, Mia Vallens, to help him speak with his mother. Mia agreed and shapeshifted into Kelly's form. Jack spoke with "Kelly" who told him that what he was didn't matter, it's what he did. She encouraged him to believe that even monsters can do good in this world.[4]
Jack and Sam Winchester
Jack and Sam
Sam is the first person Jack encountered after he was born. When they first laid eyes on each other, Jack was mostly obscured by shadows in the corner of his nursery, and he gave Sam a creepy smile, frightening the hunter.
Jack initially mistook Sam for his father and Sam had to correct him. To avoid conflict, Sam tried to speak calmly with Jack to let Jack know he didn't mean the newborn any harm. Sam's plans were torn apart when Dean decided to shoot at Jack.
Jack fled and the brothers pursued him. Sam believed Jack was not an evil child and he sought to have a proper conversation with him. Once the brothers found him at the Sheriff's office, Sam stunned Jack with a taser after which the two ended up in the holding cell. Sam was terrified of Jack once more until Jack reassured him that he wasn't using his powers on purpose.
The two began to converse and Jack announced his desire to find his father so his father could protect him as his mother promised. Sam told Jack that his father - meaning Lucifer - didn't do that but Jack corrected him, saying he meant Castiel. The two soon got into a fight with angels who had come to claim Jack. When one angel tried to kill Jack, Sam was forced to kill her, only to remove the angel blade from his chest unharmed.
Jack joined Sam and Dean in burning the bodies of his mother and "father". Jack didn't know what to do say, so Sam suggested saying "sorry" and "thank you".
In contrast to Dean, Sam supports and believes in Jack becoming a good kid who simply needs to learn how to use his powers. Sam makes an effort to help Jack in this regard and also remind him that Jack is not evil. Sam however, does seek to use Jack's power in freeing his mother from the alternate universe. Sam admits to this when he is questioned on his motives. Sam tells Jack that he won't force him to try and continues to encourage Jack to believe in himself.
During a case involving a shapeshifter, Jack saves Sam's life by stopping a bullet fired by the shapeshifter Buddy from hitting Sam.
In Tombstone, Sam quickly deduced Jack was responsible for bringing Castiel back. Sam was proud that Jack's powers did good as brought back an old friend and moved Dean out of his depression. Sam humored Jack in his supposed hunter case however, he saw Jack was right about it being a supernatural creature. When Jack tried to help Dean in fighting off a ghoul, Sam and Cass warned him but to no avail as he used his powers and killed an innocent as well. Jack was horrified as Sam tried to reassure him but he couldn't get through. On the way back, Sam tried to console Jack after his accidental killing but the latter angrily tells them to stop. This act caused Jack to leave the group out of fear of hurting them.
In The Bad Place, Sam is reluctant to believe that Jack killed Derek Swan and that he must be killed. After Jack is determined to be innocent, he reveals he was using his powers to search for their mother and located her, letting Sam and Dean realize she was still alive. On the drive, Jack states that he sees the Winchesters and Castiel as his family while Lucifer and the angels are nothing to him. Sam is visibly pleased by this and the fact that Dean instantly agrees that Jack is their family. At the end, they are sent to separate realities.
In Wayward Sisters, Sam questioned Kaia Nieves of Jack's whereabouts and is told that he is with Mary Winchester in Apocalypse World, to Sam's worry.
In Breakdown, Sam enters a depressive state at Jack being gone as he and Dean have lost another important person, as well as hope for finding their mother.
During Devil's Bargain, Sam and Dean are told by Castiel that Michael is the that world and he intends to invade. They realized Jack and their mother are in danger and they decide to capture Lucifer and open a rift to enter the Apocalypse World to save the pair.
Jack and Dagon
Dagon aspired to be Lucifer's Queen and Jack's mother. To this end, she took care of Kelly Kline during her pregnancy. Dagon initially treated Kelly with a degree of hospitality and did her best to prevent Kelly from being found and kept anyone - such as Dr. Turner - from realizing the uniqueness of Jack.
Dagon began mistreating Kelly after Kelly allowed herself to be lured away by Dean Winchester. Kelly's days spent with Dagon became difficult and stressful, until Jack reassured Kelly that her suffering was not for naught. Dagon lost sight of Kelly again when angels led by Castiel raided her hideout and took Kelly away. In fear of Lucifer's wrath, Dagon sought out Castiel's destination by torturing Kelvin.
She arrived in time to stop Joshua from killing Kelly and her unborn child. As Dagon proceeded to beat up Castiel, Jack gave Castiel some of his powers so Castiel could incinerate Dagon. Dagon's dreams of being Jack's mother were burnt away by Jack himself.
After being born, Jack showed little remorse for helping Castiel kill Dagon and even called her "a bad woman". Dagon is the first being killed because of Jack.
Jack and the Angels
| “ | I am home. | ” |
Being Lucifer's son and a Nephilim, Jack was considered a great threat to all those around him, including Heaven who, like everyone else, feared what would occur after his birth. Before his birth, the angels sought to kill his mother Kelly Kline to prevent her son from being born but she was protected by the efforts of the Winchesters and Castiel. After his birth, the angels now view Jack as a necessity to the survival of their race as after Fall of the Angels their numbers have been greatly depleted. The angels pursue Jack as they believe he has the power to produce new angels therefore, replenishing their numbers, to that end they sought out Castiel in War of the Worlds to get him to convince Jack but he refused to let them near his ward. Castiel also learns that the angels plan to use jack whether he wants to or not. In The Bad Place, the angels kidnap Kaia Nieves, a dreamwalker Jack had met so they could convince him. Once Jack and the Winchesters found them, the angels try to get Jack to come to Heaven with them to be with his family.
Similar to Lucifer, Jack does not see them as family and denounces the angels as killers even killing one that was attacking Dean.