Relationships
Sheldon's closest friends are Leonard Hofstadter, Howard Wolowitz, and Raj Koothrappali. Of the three, Sheldon is openly dismissive of Howard and constantly opines that a master's degree in engineering demonstrates a lesser intellect than that of the others, who all possess science doctorates. Despite that, Sheldon has referred to Howard as a "treasured acquaintance" and later his friend at various points. Sheldon constantly belittles Leonard and dismisses his work, yet at the same time considers Leonard his best friend, as they used to live together and can tolerate each other: in "The Space Probe Disintegration", Sheldon admits to Leonard that he is aware of how difficult he can be, and tearfully expresses his gratitude for having Leonard in his life in spite of himself, causing Leonard to break down beside him. Prady stated that "the fact that, despite everything, Leonard considers Sheldon his best friend reminds us of Sheldon's essential humanity".
Leonard has stated in the series that he and Sheldon have a dysfunctional relationship, one that many times people have mistaken for a romantic one. People most likely assume that due to their familiarity with each other. Because of Sheldon’s strange tendencies, they know each other’s bathroom habits and schedules, among other things that ordinarily roommates would not know about each other.
Sheldon can only handle having a limited number of friends in his life at a time, but later shows flexibility when he accepts Bernadette and Amy as part of the social group. In season 6, the guys ask if comic book store owner Stuart can be part of the group while Howard is in space.
Despite Penny's neither being a scientist nor sharing many of the group's interests, and having constant fights with Sheldon in the early episodes, they become close friends. While some fans supported a romantic relationship between Sheldon and Penny, Lorre stated his opposition to it by saying: "We've stumbled into creating a character who has chosen a lifestyle for himself that is unique. And I don't see any reason to modify it."
He once idolized fictional prodigy Wesley Crusher from Star Trek: The Next Generation, portrayed by Wil Wheaton, until Wheaton did not show up at a convention attended by Sheldon in 1995. Sheldon had spent 15 hours on a bus travelling to the convention during which time he was forced to break his rule about urinating in a moving vehicle. After this moment Wil Wheaton became number six on Sheldon's mortal enemy list (a list he started when he was 9 on a 5¼-inch floppy disk). Wheaton was one of Sheldon's mortal enemies, along with his coworkers Barry Kripke and Leslie Winkle. Later, Wheaton managed to patch things up with Sheldon, only to inadvertently pass the enemy list spot to Brent Spiner, who removed the packaging from a signed Wesley Crusher action figure presented to Sheldon as a gift. Sheldon would later resume his enmity with Wheaton in season 11's "The Proton Regeneration" when they compete for the lead role in an Internet reboot of Sheldon's childhood favorite science TV series, Professor Proton, with Wheaton getting the part; however, when he sees how well Wheaton plays the role and on the advice of Howard, he apologizes to him.
In the season 3 finale, Howard and Raj blackmail Sheldon into meeting Amy Farrah Fowler, with whom they matched him on a dating website. After some obnoxious comments about the dating website, Sheldon finds that Amy agrees with him, and he grows fond of her when she says that "Any or all physical contact up to and including coitus are off the table". Their relationship continues in season 4, although Sheldon often points out that they are not in a romantic relationship (stating that she "is a girl who is a friend, but is not my girlfriend"). The two enjoy intellectual games they create, and Amy and Sheldon openly express the same type of intellectual superiority.
In season 5, when Leonard inadvertently implies that he and Amy may have had sex after a wedding reception that they both attended, Sheldon unexpectedly reacts violently, karate-chopping Leonard's neck while telling Leonard "She is not for you... not for you!" Later, Sheldon formally asks Amy to be his girlfriend in "The Flaming Spittoon Acquisition". During their relationship, Amy begins a campaign to give Sheldon more attention to increase his feelings for her by embracing his interests. As they watch Howard being launched into space in its season finale, Amy is surprised when Sheldon takes her hand for emotional support.
During the first half of season 6, in "The Parking Spot Escalation" and "The Fish Guts Displacement", Sheldon is pushed further after seeing Amy partially exposed and taking care of her while she is ill respectively. In "The Cooper/Kripke Inversion", after being directly asked by Penny if he would ever have sex with Amy, Sheldon admits to Penny and Leonard that a physical relationship with Amy is a possibility, and being touched is something he is working on. While upset about Kripke, Amy does give him a consoling hug that Sheldon seems to need, and want. Even so, Amy has offered other romantic physical contact, and was very uncomfortable when they had to cuddle. In "The Spoiler Alert Segmentation", Leonard temporarily moves out and Amy proposes that she would be his perfect roommate and tries to move in, though Sheldon is uncomfortable with this change in their relationship. While playing Dungeons & Dragons during "The Love Spell Potential", Sheldon's and Amy's characters are commanded to have sex within the game. A very upset Amy asks Sheldon if they are ever going to be intimate and he again admits that it is a possibility.
In season 7, Sheldon passionately kisses Amy on the lips for the first time. Initially to prove a point, he later prolonged it, implying he enjoyed the feeling. Later episodes showed him willingly kissing Amy, implying he has gotten more comfortable in such a position of physical intimacy. The ultimate proof of Sheldon having feelings for Amy is given in the season 8 episode "The Prom Equivalency", when he finally admits being in love with her: "I love you too. There's no denying I have feelings for you that can't be explained in any other way. I briefly considered I had a brain parasite, but that seems even more far-fetched. The only conclusion was love." In the season 8 finale, "The Commitment Determination", Sheldon and Amy get into a fight over their definition of "commitment". Sheldon feels his relationship with Amy is going fast on its own, but Amy argues he is taking things too slowly and does not properly bestow on her unlimited affection. By the episode's end she has decided to take a break from their relationship while Sheldon is left numb from Amy's revelation. He glumly reveals that he had been planning on proposing to Amy with his grandmother's ring - a family heirloom.
In the season 9 premiere, Sheldon keeps pushing Amy to make up her mind about their relationship, but goes too far and insults her to her face and she angrily breaks up with him for good, thus officially ending their relationship. In "The Perspiration Implementation", Barry Kripke learns that Amy is no longer in a relationship and implies an interest in asking her out on a date. Sheldon is bothered by this notion and challenges Barry in a duel that will end three years hence. In "The Platonic Permutation" Amy offers Sheldon a chance to get back together with her after spending time together in an aquarium at Thanksgiving, but learns that he simply just wants to be her friend, with him revealing to her that "I excel at many things, but getting over you wasn't one of them". In "The Earworm Reverberation", Sheldon cannot get a song out his head, but after suddenly remembering the title and the lyrics, he realizes that the song was about Amy and that she changed his life for the better, which prompts him to go to her apartment to profess his love. He finds Amy on a date with Dave, who has a great adoration for Sheldon because of his intellect. Seeing how much they love each other, Dave gleefully urges Sheldon to kiss Amy, leading to their reunion. In the following episode, "The Opening Night Excitation" Leonard, Howard and Raj go to see Star Wars: The Force Awakens without Sheldon as while he was initially reluctant, ultimately opted to celebrate Amy's birthday with her instead. To make Amy's birthday enjoyable and memorable, Sheldon seeks out Penny and Bernadette as he respects their opinions regarding all things socially appropriate. He reveals to them that he has narrowed things down to three options, the first being a chance to play the harp with the Los Angeles Philharmonic, the second being an all-expense-paid trip to the Wisconsin Sheep and Wool Festival (though Amy would have to go alone because Sheldon's ornithophobia is nothing compared to his fear of sheep), and the third being the two of them engaging in coitus, at which point Penny squeezes and shatters the wine glass in her hand due to disbelief and/or shock. After Penny and Bernadette convince him that finally being intimate with her is the most beautiful gift that he could give to her, Sheldon and Amy have sex for the first time on the latter's birthday. Sheldon comments, "I enjoyed that more than I thought I would".
In season 10, Sheldon and Amy move in together for a five-week experiment to test out their compatibility, and after its successful run, decide to move in together permanently. In "The Holiday Summation", Mary Cooper confesses to being accepting of Sheldon and Amy living together out of wedlock in the privately held belief that Sheldon would never be in a relationship, which deeply offends him. In the tenth-season finale, Sheldon unexpectedly proposes to Amy after being kissed by Ramona Nowitzki, a graduate student who had been infatuated with him in earlier seasons. In the eleventh-season premiere, Amy accepts his proposal, and they marry in the season finale. Late in season 12, Amy is preparing Sheldon to accept the prospect of having children by getting him to have fun experimenting with the Wolowitz children. In the series finale, both Sheldon and Amy are recipients of the Nobel Prize in Physics for their discovery of super asymmetry which they first worked on moments before their wedding. In Amy's speech, she encourages young girls around the world to study whatever they want. Instead of giving a self-centered speech, Sheldon thanks his family, his friends and his wife Amy for always supporting him. He also refers to Howard as "Astronaut Howard Wolowitz", exhibiting, for the first time, some level of pride in having a friend who was an astronaut. He also admits that he agrees with what Leonard said in the pilot episode, that Leonard and Penny's children will be "smart and beautiful".
At the end of season one of Young Sheldon, the adult Sheldon refers in voice over to having had children: in season 4, it is revealed that one of them is a son named Leonard, and banter between the adult Sheldon and Amy implies that their son was meant to be named after both Leonard Hofstadter and Leonard Nimoy. In the series finale of Young Sheldon, it is revealed that Sheldon's other child is a daughter, and that Sheldon's children appear to have interests contrary to his, such as athletics and acting.