Based on a Korean novel
Found the novel on Reddit.
Red/black flag ml, "anti-social disorder", disability to feel empathy or something, treats mc like shit (rapes, degrading, humiliation, etc.) and then he's "kind" and cycle repeats. Mc loves ml unrequitedly since high school and stalked him to get revenge for his best friend. Mc always "forgives" ml bc he doesn't have anyone else, too "nice", and he loves ml. Happy ending ig... Still hate ml..
Tappytoon
Heard it's sad
Red Mansion