Am I Losing The Fight?

There is so much shit on my mind right now. I call myself a man and im not even in control of my own life. I let life control me. Me and my fiance have been through so much in our year and a half relationship. From lies to deceit, yelling to name calling and etc. Things dont seem to be getting any better. What am i to do. She is the mother of my beautiful daughter and is ginuinly a nice person. But how much is too much. I cant leave her without thinking that she may be thinking of somebody else. Is it that we are too different? But i always thought opposits attract.................................... i guess not. Today she started to give another man her, no, our phone number and I'm just thinking to myself, "What the hell kind of shit is this". is this what a relationship is supposed to be. All these up's and down's. This is too hard for me. I have never had a relationship to work in my favor. And I dont ask for much. Just respect me and I'll do my best to keep you happy. I guess karma is coming back around from my childhod because i was an asshole. Now all i seem to pick up is assholes. What am I to do? I need some answeres....................... some help!