Spoiler from novel

Based on novel (maybe differ from webtoon?).

Uke wasn't gay at all. In novel uke is kinda loner so he admired seme who he thought was cool. He thought by following seme around he had his secret not that he wanted to blackmail seme. He just feel connected (kinda like Oh I feel special because I m the only one who knows). Seme has positive reputation at school. This stalking habit became hsi routine.

Seme is chaebol, his family is normal chaebol. But his grandfather is gangster. Seme is well liked by his grandfather because seme has similar twisted mind as him. Seme is gwanggong & psychopath.
Even after seme assault, he tried to control uke. He forced uke to stop his part time job tutoring by giving uke his card. Uke secretly rebelling by keeping his jobs. So seme sent his underling to threaten uke's bosses. Uke than use seme's card, but the card has been cancelled. It made uke to beg seme. Uke is sole bread winner in his family. Uke the forced to sleep with seme on the day he usually he went tutoring.

Uke is afraid of seme. Who got beaten up by seme if he rebel. Uke brother was in huge debt and he ran away to Vietnam or Philippines (don't remember). One day, hyung came back and forced uke and the mother to ran away abroad with him. Of course using uke saving. Uke tried to call seme and tell him that the loan shark are after his family so he have to leave. But hyung snatch his phone and destroy it. They were captured by loan shark and they were about to be harvested (their organ).

Seme who can't call uke, looked for him at his home and found uke phone was broken. Finally seme arrived at where they were kidnapped. Hyung is already at operating table, mom was passed out. Uke is still awake. Seme found him and got angry. Seme knew uke was kidnapped, but he still blame uke for ran away. He smashed uke angkle.

Uke was given option, uke have to stay with him and live with him or else he will make uke family suffer by sending him the loan shark. At this point the dynamic of their relationship is : uke scared of seme, seme is obsessed over uke but never say he love him or something.

After few weeks not able to leave seme house, mom is invited to seme house. Mom was worried because his broken ankle and ask where will he come home. Uke told mom he can't leave because loan shark will come looking for them again. And only by living by seme side they are all will be safe. Mom understand that uke was held hostage. She said it's okay and still asked uke to come back home. Uke afraid that seme will be angry. So uke told his mom, seme is his lover. And he didn't work for months and all his money are given by seme. Mom was shocked but she understand.

I think if I m not mistaken, uke started liking seme when side story begin. Seme was booking a vacation with uke. But the agency name is a girl name. Uke thought seme was cheating, and he was angry, he yell at seme. Seme wanted to beat up uke but realized uke is shaking in fear so he asked him what him. Uke told him he saw his text message with a girl. Seme looked at his phone and it turned put a misunderstanding. I think this is the first time seme can hold his fist back.