First of all, no, just because two guys have sex in the story somewhere that it should be classified yaoi/shounen ai no matter the context. That is why a story can show you some insane scum kidnapping and raping women in a story and as long it's being depicted in a way that only invokes shock, repulsion and fear, it gets a psychological/horror but not romance. But this one is yaoi because yeah, the dynamic between that monster and his victim is very focused on pathological romantic attachment and the intent of the author is clearly to portray an extremely toxic romance. The emotional crux of the story, from what I can derive from the comments, was to make people pity both the characters and grieve over how they could have had a healthy relationship if not for this and that. Even if this was straight, it would probably have a romance tag alongside psychological.

Why tf is killing stalking in the top 10 yaoi? It’s a psychological thriller and has no real elements of yaoi except boys kissing a few times.