Pretty sure, HE didn't abuse Seungho sexually. More like he found him and Jihwa kissing and than tried to first beat the gay out of him and when that didn't work turned to have him medicated to 'cure' him.
What you could be very right with however is, that his father might have forced him to sleep with female prostitutes/courtesans to try and steer him on the 'right path' again. Which actually would translate to sexual abuse/rape as well and if the father instigated it, he was responsible for it even if he wasn't the one actually doing the fucking.
And when he was old enough, Seungho said fuck it and did everything he could to both slight his father in any way he could and finally do what he was forbidden to do for all that time: have as much sex with males as he wants to have no matter if everyone knows it.
His father actually made everything worse lol. If he had done nothing, the worst possible outcome would have probably been Seungho and Jihwa continuning to kiss maybe fuck but they would have at least done it in secret. Now everybody knows because Seungho takes special care to let everyone know about it just to spite him.
then*
Mmm, IDK about y'all but I ship Jihwa with that hired killer. The guys is sculpted af.. I just hope he doesn't kill the painter though..
On the other hand, I think his father did something horrible to him, idk like, sexual abuse? Or he made Seungho enjoy the "company" of girls and they kinda forced him to have sex with them, hence Seungho's preference for male partnerd bc he's extremely disgusted with females.. IDK just theoryyy