seperated? married? confuse

Okay so I've been talking to a guy he's married but here's the thing he is seperated from his wife. Its gonna be a year since they've been separated. He has his own apartment and well she stayed in the house obviously, he has kids which I'm good about it. However, this lady is crazy. I just want to understand I know that he still married and he will eventually get divorced but is it bad that I want something with him even though he is separated? I mean we talk everyday he's very nice and not to mention but he had a rough time with his exwife where dhe just humiliating him in the worse ways you could imagine. I know he wants to be with me and I want to be with him. But this lady has gone beyond the line. 
EDIT: 
I understand all of that. He is in the process of getting divorce but it is hard cause he lives by checks which he doesnt have enough money and he gives her for the kids. She takes advantage of him and I've told him. He knows that. He only wants the best for the kids. I've pushed him towards the divorce but like ai said money is a problem since he lives by his checks. He's saving up money for the divorce.