
Just because dong huyn says it doesn't mean author meant it . It is just an opinion of a character who knows nothing about the main couple.
Taesung is possessive and insecure when it comes to sooyoung that is why he hides his past. He didn't beat sooyoung, kang il did . Taesung knew it was gonna happen but he arrived late on purpose because he wanted sooyoung to know what it feels like to get hurt intentionally ( remember that sooyoung likes to get punch-drunk as the doctor said)
This is not sexual abuse . It's consensual

"remember that sooyoung likes to get punch-drunk as the doctor said"
Apparently you don't know what "punch drunk syndrome" is. It's a condition seen in boxers caused by repeated blows to the head. Basically the doctor said that his brain is damaged and he should take care of himself because it will get worse.

I wasn't clear enough. If you look at sooyoung first meeting with taesung ,where sooyoung beats the shot out of taesung, you will notice that sooyoung ,throughout his life, has been struggling and punching as if punching the air, and he invites being punched and getting hurt. An example would be when first taesung brought him to his office and some hooligans just tried to beat sooyoung . Minhuyk was shocked at sooyoung's resilience. Not only his brain is damaged but he also doesn't care about getting more injured since it was his way of coping with his abusive father
People keep trying to justify Tae Seung's behavior and saying that there's no abuse. Even after the author spells it out in the last chapter by Dong Hyun saying "Clearly this is abuse". Because of his work DH has plenty of experience dealing with abusive assholes, that's why he knows exactly what abuse looks like. And he was there when Tae Seung pretended to save Soo Young when actually he was the one that allowed those guys to beat him up .