Yeah, Dojin was in the wrong because of his actions, but he is actually proving to be a really promising father. I feel really bad when Dojin is getting poor treatment. Hyesung has a right to be angry, but he isn't fully innocent either. Since Dojin is trying to better himself and show effort, the least Hyesung could do is not act like a fucking brat all the time.
spoiler- okay to be honest I was disappointed with what MoLahn said, but if we look at his character, he was odd from the beginning. In the first place, he saw a random person and slept with him right away, so his question seems to fit his personality type (at least for now). we can expect a background story that explains it, and we will probably see some character development for the love story. keep an open mind!( ̄∇ ̄")