It's pretty realistic of men with internalized homophobia, ashamed of their BDSM kinks, and have never had a healthy childhood and healthy emotional development.
He's not homophobic. True he doesn't understand bdsm and even sadism, but my problem lies with his intense negativity towards Sodam for not salivating over him from the start too. He immediately jumped to fantasizing about hurting him, and even when he learned Sodam was trying to PROTECT him, he still wanted to cause Sodam physical and emotional pain and humiliation out of REVENGE for not liking him best (hence incell behavior). Not self hate, revenge.
Preach
This story is fucking trash. Hajoon literally can't make up his dumbass mind. It's really really bad writing. His character is all over the place. He's like an edgy little incell spewing cruel things at Sodam and the chapter ends with him realizing his psycho thoughts were unwarranted because Sodam was protecting him. He hates Sodam for not fawning over him back then yet he is NOW and it's not good enough.