beta
Edited since I skimmed through the raws:
The way I understand it, the conflict is basically a complicated love rectangle(?) between the four characters, but specifically the core of it is the triangle between Daon, Jaemin, and Soohyun. Soohyun has an extreme obsession with Daon, who has a crush for Jaemin, who in turn has feelings for Soohyun. Both Soohyun and Jaemin know that Daon likes Jaemin. Soohyun, a scumbag that he is, uses this to keep Daon chained to him always, by threatening Daon he'll get together with Jaemin should he not reciprocate. He even once went as far as kissing Jaemin in front of him with the only intent of hurting Daon for not showing interest in him. By the look of it Soohyun has no interest in Jaemin whatsoever, but he loves to use the "I'll date him" card to threaten Daon into complying to his will, who falls for it everytime. His weapon of choice against Daon is basically just, "well, if you don't wanna be my boo then I'll just go after your crush instead how about that lol?"
On the other hand, Jaemin, who also knows Daon likes him, is stringing Daon along out of his resentment toward him for having Soohyun's interest, and just keeps him around to keep him away from Soohyun.
Seunghyeon is simply just thrown into the mix since he has a crush on Daon, hence turning the triangle into a rectangle.
Both Jaemin and Soohyun are super toxic and manipulative, I pray Daon would snap out of it soon and steer clear from them.