I get the whole abusive family fucked up attachment shit. He doesn't want to be alone so literally anyone (even the deadbeat dad) will do.
But we know he would have had Sihwa by his fucking balls if he so much as touched his father. BUT His father critically injuring Sihwa with a fucking golf club to the head is okay? The father didn't know he was an alien so like he actually almost committed murder and tried to run away? Wtf. What the actual fuck is wrong with this story now.