It's not because of his mom's remarriage. Go back and read the high school flashback in chapter 18. Most likely Woojin found out about Wooyeon being gay or something else and bullied him, Wooyeon got into argument with him and everyone started blaming him instead of Woojin and bullied him by talking nasty about him, ruining his stuff and writing things on his books and locker
He could have made some assumptions/jokes back then but still there could be other stuff that made their relationship go downhill. There could be some inferiority complex weighing on Wooyeon especially judging by how people made assumptions about him in school whenever Woojin was involved. Regardless of how fucked up they both are, Woojin is a piece of trash because what he has been doing so far is the worst type of raping
woojin is horrible for the hypnosis thingy but out of the playtime why wooyeon is so mean to him? i mean he's mad cuz his mom remarried and he got a new brother but his attitude even escalated till he's in university? doesn't make sense