What do you mean? She's clearly in a mental hospital right now. What else can he do? If you mean earlier, the hospital told him that she was fit to be released and he believed them. That's not necessarily his fault either.
What the father can do is keep Doo-joon away from her. Hae-in burst out of there believing he’d be there to visit her, since her father told her so. However, since it’s obvious she isn’t cured yet, bringing Doo-joon to her would just worsen the problem.
He's definitely in the wrong for using Doo Joon's name to be able to see her but he clearly wasn't going to bring Doo Joon to meet his daughter. Doo Joon won't go anywhere NEAR her in the first place, making that an impossible situation. Lying to his daughter to see her doesn't make him a bad person considering that it's not harming anyone, it just makes him sad, maybe even a bit pathetic. If he let her out of the mental hospital after all this then yeah, THAT would make him a shit person.
It harms his daughter. She got her hopes up all for nothing, and in the first place, why would he think it’s a good idea to use Doo-joon’s name in order to go see her? She was obsessed with him to the point where she broke into his house. Anyway, Hae-in’s father is still an irresponsible father to me. While I can UNDERSTAND his point of view, that doesn’t justify his actions.
Why is Hae-in’s father so irresponsible? I get that this is his only child, but can’t he understand that Hae-in and Doo-joon need to be kept apart? She needs therapy, and a lot of it. I agree that it’s not entirely her fault as it’s a mental illness, meaning her father needs to get his shit together and face the fact that his daughter is causing a disturbance to others’ lives.