Should I let the girl I love go?

So I love my girlfriend, but we had a problem so I thought it was best to end it between us, a short while after I ended it, two weeks later she got back with her ex. Then she said she still loves me and doesn't know why she was with him, so she slit up with him and maybe 3 weeks later we got back together. The problem is, she has so many lads that like her, and when she's with them lads she doesn't even text me, it's like she just blanks me. She took a lad who's she's going to a concert with back home with her and now she's blanking me again. I don't know what to do, I want to trust her but how can I? The first time I was with her she said he would never get back with her ex because she knew it would hurt me, but she did get back with him and it did hurt me. I lost trust with her because of that and now I think she's cheating on me… I can't cope with a relationship that I'm constantly getting paranoid over. Should I let go and move on? Any advice would help, and don't just say yes. I need proper advice. Thanks.

If any spellings are wrong it's because I've written this on my iPhone.

I think you should honestly try talking to her, and see where that gets you. Try to figure some things out. She should try gaining your trust back if she really loves you.