Should i stay ? or leave with nothing ?

I have been with my fianc�e for 2 years and we just got engaged last month I am 21 and he is 28 I have been there for him through a lot and stood by his side even though his own father has told me he would just let me down. I have caught him cheating twice on craigslist and Facebook and did not leave and he has been physically abuse as far as elbowing me in the face and busting my lip on at least two occasions. I went through his phone again tonight and found a email from a woman saying she wanted to hook up for nsa sex and saw where he has visited craigslist again. I am torn for the simple reason he has no real friends or supportive family to help him gain back joint custody of his daughter and I have helped and done all the research and. Called lawyers and the police station and filled reports for him so he would have evidence yet he continues to stab me In the. Back I stay because I love his daughter nd him and I haven't pressed charges strictly because it would ruin him in getting his daughter and he is a great father just not so good of a fiancee or husband what should I do what's the last straw ? If I leave I start all over again an lose everything. And will have to move back with my father ...... Should I just deal with it or how can I get him to change ? Or should I just leave before it gets worse