.... did you forget Minyul tried to kill seulbee or whatever her name was. His childhood was sad, but come on, that's not an excuse to trying to kill someone over jealousy. Plus he basically got mc into that period scheme, he was going to say he could pay for both of them, but didnt because he wanted to use it as an excuse to be closer to mc. It's sad mc forgot about him after the accident, but honestly Minyul was obsessive.
Ummm.... even if he didn't lose his memories, don't you see some serious problems there? The guys is willing to go to any extend, even kill, to keep the other guy tied to him. He wants to isolate him from everyone else. In fact, he and Seolbee weren't even in a relationship. He just had a crush on her and he went off to hurt her.
Spoilers:
He ends up with glasses dude which pisses me off