<P> That night Elena comes to stay at the Salvatore house, and Stefan leaves to crash at Caroline's . While there, he and Caroline realize that Elena is sired to Damon . When Stefan informs Damon of this, they go to New Orleans to find the witch that broke a sire bond years ago that Damon had . Stefan and Damon find that in order to break the bond, Damon has to convince Elena not to care about him, and leave her, which Damon agrees to do for Stefan . Post Jeremy's death, Damon convinces Elena to switch off her humanity leading to her becoming brutal and ruthless . Stefan and Damon try constantly to make her feel something again . Later after Elena's humanity comes back, she chooses Damon, leaving Stefan heartbroken . Then Stefan tries to dump Silas body in the river only to find that Silas is still alive . Silas then reveals that Stefan is his doppelganger . Silas was the one who created the immortality spell 2000 years ago however, as nature creates a balance for everything, it created a version of Silas that could be killed, a shadow - self which ends up being Stefan . Silas then locks Stefan into a vault and drowns him in the river . This incident tempts Stefan to turn his humanity off in order to escape . Stefan happens to be in the safe for 3 months where he keeps on hallucinating . </P> <P> In season 5, Damon and Elena manage to figure out that Silas has taken Stefan's place and that Stefan is in that safe . When they go to rescue him, Stefan isn't there . Instead, a very powerful witch (Qyetsiyah) had opened the safe for him and fried his brain due to which he suffers from amnesia . Qyetsiyah (or Tessa) loved Silas but on the day of their marriage, he cheated on her and took the immortality spell for the women he actually loved, Amara, the original doppelgänger of Elena . Stefan returns to his old ways but when he saves Elena from Tessa, she wants revenge so he gives Stefan his memories back which gives Stefan Hallucinations of the safe . Caroline tries to help him but when that doesn't work, Katherine comes back in the picture and manages to cure Stefan but they have a one - night stand, which leads Katherine to believe that Stefan still loves her, however he rejects her . Later on, Katherine takes over Elena's body and breaks up with Damon so that she can get Stefan . After trying to woo him and failing, Stefan realises that Katherine is pretending to be Elena and Elena is with Nadia, Katherine's daughter . They rescue her somehow by killing Katherine and sending her to some sort of hell . Then Stefan volunteers himself to the travellers to give his blood as they needed doppelganger blood . Caroline and Enzo try to find and kill Tom Avery, Stefan's last doppelganger in order to save Stefan and they succeed due to which Stefan and Caroline grow even closer . Near the end of the season, Stefan and Elena keep seeing dreams of the two being together and of them as humans . They work out that the travellers planted those dreams there as it was always meant to be Stefan and Elena not Damon and Elena . Through the fight, Stefan and Elena are kidnapped by the travellers as they need their blood to finish their spell . However, Enzo and Caroline save them by killing Tom Avery, Stefan's doppelgänger . In 5x21, Stefan tries to save Caroline's life from Tyler (while a passenger, Julian, is in his body), during which Tyler kills him, sending him to the disintegrating Other Side . In the episode' Home' he is Resseructed because Liv did a spell due to which he and his other friends can get back but Damon and Bonnie are left there leaving everyone broken . </P> <P> In season 6, Stefan moves away from Mystic Falls because of Damon's death and finds a new girlfriend called Ivy . However, Enzo and Caroline, find him and Caroline tells Stefan that he's a coward and the worst friend ever . She starts crying so Enzo goes and kills Ivy . Stefan vows revenge . He comes back to Whitmore, and uses Elena's help to find Enzo leaving him to be killed by a vampire hunter . However, Enzo survives . Ivy returns as a vampire and it is revealed that Enzo had fed her vampire blood against her will before killing her . Damon, then returns to Mystic Falls and meets Stefan first which brings Stefan back to his friends . To make things worse, Enzo tells the other vampire hunter about Ivy and all the other vampires and the vampire hunter kills Ivy but is killed by Damon before the vampire hunter would kill anyone else . Enzo, figures out that Stefan's niece, Sarah is alive and that Damon had thought that he had killed Sarah before she was born but Sarah was born before her mother died however, Stefan kept this from Damon and Enzo uses this against Stefan . Meanwhile, the vampires have another threat, a psycho killer, Kai . Added on top of that, Sheriff Liz Forbes (Caroline's mother) is diagnosed with cancer . Stefan supports Caroline through this in which they bond even more and share a passionate kiss however just then Liz dies . At the funeral, Stefan realises that he has fallen in love with Caroline but before he can confess, Caroline switches off her humanity switch after the funeral . Stefan and Elena try to bring Caroline back but it fails and Caroline vows revenge for them not giving her the year she wanted without any feelings . She kidnaps Stefan and Damon's niece, Sarah Salvatore, and blackmails Stefan to turn off his humanity to save her . At the end of the episode' The Downward Spiral', he does and joins Caroline . Stefan decides to ruin Caroline's life because she has done the same to him . He wants her to lose control and become a Ripper . He eventually is able to and they sleep together for the first time . When Lily, Stefan and Damon's mother, is rescued from the 1903 prison world and turns out to be a vampire, she manages to turn on Stefan's humanity again . However, it later is revealed that Lily lied to get him back and doesn't love her sons any more and only wants her travelling companions back . Stefan then pretends to still have his emotions off to get Caroline back and somehow succeeds, but Caroline tries to avoid him as she feels guilty for everything she had done . Stefan then also tries to talk Damon out of being a human again only to be with Elena but Damon decides to take the cure . </P>

When does stefan turn his humanity off in season 6