How long do you fight for an unhealthy marriage?

I by no means am faultless in life and in my marriage, but at what point do you decide that enough is enough? He hasn't stepped up to provide for our family us two, one on the way and our daughter. He gets mad when I talk about getting a job to help. He is shut down, only shows interest in me when he wants sex... I feel used, never go out on dates. Always leaving to go places without family and without me, working overnight or going back to work to work extra hours after a normal shift. Before he left for army training, he got so mad at me he was swerving all over the road, screaming and cursing at me, in my face, threatened that he would f my world up. It came out that he'd lied about getting into running drug money, lied about other things. Well then he left and it comes that he's been messaging a girl and planning times to hang out with her before he left, all during times he was working and didn't want to be around me or his daughter. I confront him, he swears she's a friend and writes a thoughtful letter home about how he has never cheated and has never even thought about it. Well then it comes out that his last semester in college 8 months ago, he withdrew and I had no idea because he was always leaving and going to school, and study groups and exams... If he dropped out, where was he going? And then I find he has an account on a private message/hookup site.

I feel so extremely embarrassed, heartbroken, angry, betrayed... I feel guilty for putting my children in this situation, I feel stupid for not seeing all the signs... him slamming his hands on the walls next to my head and screaming over me and calling me names. Now I'm in this extremely complicated, involved scenario where our babies will be affected. I am so mad at myself for not protecting myself and them from this... Do you keep trying, do you decide to back out and find happiness. I've been abused by my step dad, step brother and exes... If this marriage fails... I don't know that I'll find anyone that will love me. Let alone the "baggage" I carry. I don't even know where to go from here. What can be repaired and what can't?