Girlfriend cheated on me and said it was a mistake and is always starting arguments and says she don't mean too, what do I do?

Simple, if you can't trust her then it's game over.
Time to move on..

I'm trying everything I can to forgive her and it's easier said then done to trust her but I'm willing 2 try everything I can to rebuild don't don't feel like she's trying as hard as me,

Maybe she just doesn't want to be with you. People just don't cheat for no reason. Sit down and talk to her about it. Let her know everything you are feel and listen to her feelings and concerns about the relationship. Then you both need to take some time and decide what you want to do from there. If you do stay together it needs to be a fresh start. You need to trust her completely or don't bother continuing the relationship. And you can't bring her cheating up every time you get into an argument. Consider if you can handle doing those things and forgiving her when you are deciding if you want to continue the relationship. Good Luck!

How can you possibly forgive without knowing why? Then you can decide if she is worth your effort. Until then, there can be no rebuilding or gaining trust without honest communications, and even then it will take time.

What's the arguments about, you asking her about the cheating?

The reason she cheated was because I was never around and didn't show her any attention, it was my mate that was texting her and made her feel special sending nice texts while I was at work, But he's know to try it on with his friends girlfriends but never thought he'd do it to me! We argue about me always asking who she has seen at work and what she's been doing that day, I'm just worried about her becoming close friends with a guy in case it happens again, people said to me that she's 19 and just learning from her mistake but that's a mistake you shouldn't need to learn from!

Sometimes when a person cheats, they do regret it because it hurt you and your relationship. However, even though they regret it and hate themselves for cheating and hurting you, they sometimes still may not want to be with you although they are sorry. My advice is to just ask her what she wants. If she says she don't want to be with you anymore, then forget about her. But you can't stay with her, fight after fight, and not do something about it. You need to follow your own happiness, and do what is right for you.

A relationship can't survive without trust. Even if you say you trust her you are not showing her and she sees it. Stop questioning her every move and who she's with if you still want her. I know that you are tryings to make sure it doesn't happen again but if you keep demonstrating that you don't trust her it will only make her want to leave. Let her know how you feel but you have to forgive her and completely trust her if you want your relationship to survive.