Should I stay and wait this out?

Me and my daughter’s father have been together for about 3 years! He’s cheated on me the entire time, and has treated me horrible. He went to jail when I was just 4 months pregnant and got out when our daughter was 3 weeks old! While in jail, he sent me letters telling me we would be together when he got out and that he wanted to marry me! When he got out i noticed he was acting differnt. So he finially admitted to me that while in jail he started sending letter to a ex girl friend of his and that he didn’t know who he wanted to be with. Well I stayed by his side anyway trying to show him I was the one he should chose to spend the rest of his life with. After 8 months of basically allowing him to be with me and the other woman I found out shocking news! The one called me and we began to talk she told me all kinds of disappointing information. He had basically moved in with her, and was spending all his money on her. Whenever I told him about the coversation he began to yell at me and tell me that by telling her we’d been messing around (which she didn’t know about me at all, she knew we had a child together and had thought it ended there) I had ruined his life. I was in deep depression after our split for about a month and a half. Then he came back home (he works offshore) he told me he had broke it off with her for me. I was suspcious at first but then find it to be true and everything was good for about a month. Then I found out he’s messing with his ex girlfriend from high school. She was his first love and she broke his heart when she slept with his best friend. To top it off she was now married but going through hard times. I found out that they are in the process of getting a divorce. He is telling me, my whole family, and his whole family that he wants to marry me! He’s telling me that he broke it off with her but I have reason to believe he hasn’t. I don’t know what I should do? He won’t admit their stil messing around and I’m so tired of being harrassed by her through myspace. (I’M 21 YEARS OLD BY THE WAY AND HE’S 22) I haven’t been happy with our relationship for a long time, but at the same time I’m misreable without him! His mom says that she thinks he loves me and wants to be with me but he’s just not ready to make a commitment yet. Do you have any advice for me! Should I stay and wait it out or leave him alone? PLEASE HELP ME