In my understanding of the story, Kyung soo still loves Yule, even tho Yule had done so many fucked up things to him.
Kyung Soo can't let Yule go even tho he hates him so much. That's why he moved in with Yule in the epilogue.
I personally think that this is not a Stockholm syndrome story, but a story that revolves around messed up obsession.
Just like Yule was so obsessed with Kyung Soo, Kyung Soo was also obsessed with Yule.
Both of them are so fucked up in the head
In 'what-if: Dong Hyuk', Kyung Soo kept seeing Yule when he had sex with Dong Hyuk and that he ended up feeling bad to Dong Hyuk and kept saying sorry to him in the end.
Which makes me think that Kyung Soo kinda makes Dong Hyuk as a substitute for Yule (from the very start of the story, when he confessed to Dong Hyuk)
Soooo the true ending is that he came back to Yule? Just why? I mean we see him meet with Yule in the lat chapter and they just greet each other. How come they ended up living together in the epiloque? I can see that Yule regrets what he did, he tries to terat Kyung-soo well so maybe in the future he will forgive him and even if not he still just wants to stay by his side. But I don't understand Kyung-soo he had no reason to move in to his rapists and his biggest life mistakes house. I wonder if he actually still loves him as much as he hates him. Or its a stockholm syndrome. Don't kno but I can cleraly say that Kyung-soo hates him the most and Yule loves him and wants make everyrhing up for him. I think its ridiculous I mean he turned his life into living hell. Maybe Kyung-soo thinks its his punishment, because he siad before that he can't be happy, so he stays with the person he will never be happy with? So messed up and such and unclear ending.