Eventually his personality went back to normal, and he never lost his grip on reality again. But even years afterwards, he still experienced flashbacks, and had to grab onto something solid while he waited for them to pass.
In the novel, his doctors employ a series of tactics to try to undo what the Capitol did to Peeta's brain. They bring in Delly Cartwright, a friend from his childhood, to unlock positive memories. They dose him with morphling and make him watch clips of Katniss to induce positive feelings rather fearful ones.
It took time for Peeta to break out of that conditioning, and even when the possibility existed that Peeta could be a danger to Katniss, the two of them still elected to be together and build a future in a post-Hunger-Games world. Their love for one another is evident.
Like Katniss, Peeta ended up back in District 12, which was still recovering after being firebombed. By that point, Peeta greatly recovered from the brainwashing, but he still had PTSD from having his mind hijacked. Being in close proximity to Katniss was greatly beneficial as they relied on each other to heal.
Katniss and Peeta resume their lives together in what remains of District 12, fall back in love, and move in together (although it's unknown if they got married). In the epilogue, Katniss and Peeta have two children together.
The Hunger Games: Mockingjay Part 2 Official Clip – “Real”
Why did Katniss not end up with Gale?
Katniss's focus on survival and her family's safety prevented her from fully considering romance, but her feelings for Peeta and Gale diverged in the end. Katniss ultimately chose Peeta because he understood her trauma and she didn't want to lose him, proving her love for him.
Complete hijacking requires many sessions. Peeta, after weeks of treatment (he was presumably in the Capitol for about five to six weeks total), was still able to resist the effects. He warned Katniss Everdeen of the Capitol's plans to attack her, even though his memories about her had been hijacked.
However, Peeta has been programmed/conditioned to hate Katniss, to believe that it's necessary to kill her. He chokes her, and if it weren't for someone else knocking him out, he would've killed Katniss.
we know he was injected with the tracker jacker serum and conditioned to fear katniss. under the influence of the serum, he was shown footage of her and probably the bombings in district 12 too, so he'd associate her with all these horrible things and believe she's the cause of them.
Katniss here's this and understands that even though she may not love Peeta (then) that it's one less person who has to die. (At least that's what I have always thought.) Katniss realizes that if she pretends to be in love with Peeta people will want the capitol to let them survive.
Katniss Fell in Love With Peeta During the Quarter Quell
However, it wasn't until Mockingjay -- when Peeta got kidnapped by the Capitol -- Katniss realized how much she cared about him and that she couldn't live without him.
It's only implied that they get it on via snuggling and other affectionate acts in close quarters — but if you have read the book, they really imply that they took their relationship to the next level.
What does Peeta whisper to Katniss when they reunite?
Then, he opens his eyes. He has camouflaged himself in mud, leaves, and vines. He jokes with her, whispering that it's okay to kiss him since they're madly in love, but once Katniss begins to clean him in the stream, she can see how weak he is.
While a prisoner of the Capitol, Peeta was hijacked into believing that Katniss was not human, but in fact one of the Capitol's mutts. Conversely, Johanna Mason suggested that the Capitol's torture replaced Peeta with an "evil-mutt version" of himself. This sentiment was later echoed by Katniss.
In Chapter 9, as Caesar Flickerman interviews Peeta before the Games, Peeta reveals to Caesar and all of Panem that he's in love with Katniss. Peeta's revelation sets in motion the storyline of him and Katniss as ill-fated lovers that carries on throughout the Games.
Given that she is willing to make the ultimate sacrifice to protect Peeta, it's safe to assume that the Morphling was committed to the rebel cause. Like the other victors, she knows the power that Katniss has as a lightning rod for the rebellion, and she knows that Katniss will not help without Peeta.
As she approaches him, Peeta wraps his hands around her neck and throws Katniss around the room. He begins to strangle her, nearly killing her. He is wild, unable to be stopped, at least until Boggs knocks him out with a metal tray.
Finnick learned many secrets, including that Snow, in his rise to power, poisoned his adversaries but to divert suspicion often drank from the same poisoned cup followed by an antidote that only Snow used. Segments of the propo of Katniss and Finnick are aired.
She stumbles into the snow at first, but then she dusts herself off, rises, and begins waving to the photographers, arm in arm with Peeta. The camera zooms out to a neutral angle, giving audiences a sudden, somewhat startling reminder that oh, that's right—Katniss is slightly taller than Peeta.
Katniss is told to put on her Mockingjay uniform and join Gale and Finnick for some filming of the destruction aboveground. Coin wants to make it clear that the Mockingjay lives. But Katniss can't perform for the propos because she's too upset about Peeta and grows increasingly distraught.
Peeta used the dyes to paint a picture of Rue after Katniss covered her with flowers when she died. He says he wants to hold them accountable for killing Rue, and Effie tells him that that kind of thinking is forbidden. Katniss then tells the team she hung a dummy of Seneca Crane.
Gale was responsible for creating weapons that would trigger a second wave of bombs to target first responders and combat healers. This invention potentially ended up killing Prim, but even if he wasn't directly responsible, Katniss found this tactic so abhorrent that she lost her affection for him.
