So my boyfriend and I have been on and off for many many years, and I love him with all my heart but we fight so much because its hard for me to trust him, the only reason I can't trust him is because his past! He has cheated on me before, but that was before he ever told me he loved me! He talks to his exes and other females but I always think he is going to cheat on me? What do I do? How I can I get over his past and trust him?! He does tell me he wants to marry me but also has told other females that? What do I do I'm going crazy and building up so much anger its crazy?

If he has cheated on you, he may have cheated on the others too. Words are easy to say, and for some saying that they love someone is real easy, they know what we want to hear. His actions are what will really show you if he loves you or not. Obviously those actions aren't showing love, if fact they are just making you feel more insecure.
It may be time to move on. Why drive yourself crazy, continue worrying. Life has too many oportunities to find happiness. Good luck

Wow he has so many bad qualities, does he have any good ones, or are you in love with a loser who doesn't show love, but says it? How old are you both.

My advice is to first calm down, try to relax your mind, and step back a bit. Then find some peaceful time with yourself and set aside all your feelings both positive and negative (anger, upset, confuse, hope, or else). Then start to reflect and evaluate your relationship by using your head and see it for what it really is, no feelings involved as it might lead to bias. This will help you be able to answer all the questions in your mind and might help you know what you should do.

You are the one who know him and know yourself. Think rationally regarding compatibility between you and him, who he is, who you are, can you forget all those things he did to you? It's all up to your decision.

It might be different from one person to another on what they will do when they have been lied to, cheated on, or badly hurt by someone, I had been lied to and had been used before. And No, I will never trust that person again and why should I have to trust those who did all the above to me?. normally I won't even bother continue having them or trying to keep them in my life.

I was in your shoes once, MAKE UP TO BREAK UP, that's how the history of your relationship is always going to be, Nothing but a toxic one.
Like what they say. A relationship should be a bonus in your life, not the reason of your own happiness.
You don't trust him cause of things he had done to you in the past. Without TRUST you cannot move forward with a relationship.
I know its hard to lose or even think about breaking it off with someone you truly LOVE!
Instead of thinking about gaining his trust back. Think about your future! Would your really want to spend the rest of your lifetime with a man that's treating you like this already.
Is he an asset to your future?
Go find yourself a good MAN.. the one that will treat you the way you should be treated. Being in a toxic relationship is not worth staying or fixing.

When you two broke it off, what was the reason? Why did you two got back together?
And how long was the break up?