Help me! I am about to lose my mind!

Okay my story is very long so I'm going to do my best to get right down to the point. Here it goes. I met this guy in August 2004 and he asked me to marry him February 9, 2007. Needless to say we've been together every since. I've stayed with him while he left me to pay all the bills and don't work and at one point I was paying everything for him, his 2 kids, his sister, her son, her unborn child and her boyfriend and I had to clean the house and all that stuff too. But now all we do is fight, and it's been that way for a while ... now don't get me wrong we have good days just like everyone else but things have been very different this year. In May 2008 he told me that he had feelings for someone else and I know this girl and she has even tried to be my friend and this was in 2005 and the whole thing is she was his best friends girlfriend from way back in the day. So when her and her boyfriend broke up in April 2008 she calls my boyfriend and starts playing on his soft side. Anyway i packed mine and my son's stuff and left. Well he asked me to come back and as anyone can guess I went back after he promised to end the whole thing with her. Well then the next thing you know she's playing mind games and he takes his two kids from a past relationship to see this girl ... but the thing is I've been raising these 2 kids since April 2005. And so that gets some stuff started and I just told him it's me or her and he "chose" me. So here I am thinking that things are going to be okay and he isn't having anything to do with her and June goes by and here comes July and he starts lying all over again. I find out from his uncle that he seeing this sorry ass bitch behind my back spending every hour that I'm at work with her after he drops our son off and he has the other 2 kids with they're grandparents out of town and he hasn't worked since May 27th at this point and well shit hits the fan and i flat out told him that he is just like his sorry ass good for nothing father and he was turning out just like him choosing a girl (she's 7 years younger then both of us) over me and his kids and if that's the way he wants it he will not see me or our son until he gets a damn good lawyer to take me to court and anyway so after we both have our time apart and all he talks to people and thinks about all this shit and he wants to be with me and have a family with me. Well the 2 oldest kids are now living with their mother (and I'll be posting some stuff about that whole thing later) and that is hurting both of us because they don't want to go back to her house. He hasn't talk to her in almost 5 months and well we've been engaged since 2-9-07 and he is always throwing up if things don't change we're never getting married. I don't fee like that should he should treat me this way after everything that I have done for him and his kids. So I really need help to know if I should stay and try to make things work or if I should move on or what?????? Please help me someone!