@Baek Siyun Olgami,Dreaming Freedom (seems like you've read tht lol), for like the more angst approach and less psychotic toxicity I personally liked What It Means To Be You but honestly I've not read many with these kinda tropes that are able to do it well, since there are a few that don't do it so great imo, (like My Husband Who's Lost his memories.. yadda yadda forgot the title but I found this one just plain toxic and the ml sucked) I'd say Phantom Whispers too but I haven't read that but I heard it's good 😓 idk if you've heard of this author but I liked her work a lot, Secret Alliance and Appetite. Although for Secret Alliance, it was toxic but she didn't end up with the same ml who was toxic but it did have those themes and Appetite mainly focuses on horror and the romance was a cute side genre tbh I haven't read many like this but Yh 😭
@Baek Siyun I'd also recommend Merry Psycho, To your Moralless (I also haven't read this one but it is on my reading list too 💔) sorry if I yapped a lot I was just thinking literslly off the top of my head 😭
@Baek Siyun Locked to Death/To Drown in You is one of my favorite manhwa & insanely similar to this.
basic premise is a guy befriends a mermaid who ends up being extremely obsessive, manipulative, and murderous. we basically have to watch as the protagonist's mental health spirals out of control the more and more he interacts with this mermaid. my top five manhwa of all time, sadly very underrated.
also Like Mother, Like Daughter. the MC discovers her mother murdered her younger brother. very compelling narrative where the MC tries to outsmart and prove her mother guilty.
the person above me recommended Phantom Whispers/A Ghostly Song, i second that. there's a murderer crueling killing people. the MC can hear the voices of ghosts and tries to track down the killer with their help.
lastly, Girl Under Trial/A Girl's Trial. the MC watches her handsome classmate murder someone late at night. she uses this knowledge to blackmail him into dating her. this one is fully complete with like 100+ chapters. crazy emotional rollercoaster with a morally gray MC.
@Baek Siyun If you haven't read, I'd recommend My deepest secret, The Male Lead is a Murderer, The Guy Upstairs (I think it was dropped, but I really enjoyed this one), It's Mine and Psycho (it's a bl, though).
Some are better than others, but all of them have thriller and psychological themes, as well as involving psychos interested in the main character. Might be good, specially if you are bored 😄