, you're in a tough spot right now and I can totally understand why you feel that you should give it another chance - But trust me on this, if never anything else: Don't.
I forgave my ex after having cheated on my through 2 years. I believed that it was partially my fault, and that if I had done more, she wouldn't have done it. I loved her - I loved her oh so dearly. I couldn't fathom my life without her. I wanted to take the problem on my shoulders, if only it meant that I could hug her, kiss her and be with her again.
I wanted to leave it all behind and believe her when she said that she loved me. That she would never do it again. And I did. I truly did.
But it was always in the back of my mind. Whenever she wrote a text message, whenever she took the phone in the evenings, it reemerged. I didn't dare ask her or tell her, as I would seem like the evil boyfriend who wanted to control her - So I kept it inside. I stayed my course like this for months, just for the sake of peace and love in the relationship. A chance to return to how it once was.
4 months went by and I found out, by accident, that she had been unfaithful again. It was all a lie - I had worn myself down and taken the problem on me for nothing. If you can believe it, it was more devastating than the first time. It tore me to pieces.
Now I do believe it when she says that she loves you - But not enough to never do it again. If she can do it from the start and to the end, it's simply her nature. I know you don't want to hear it and ultimately it's up to you. But you have to decide if you go the same route that I did and never completely trust her again - If that is the case, you are missing the most important part of the triforce that is a relationship; Love, respect and, most importantly, trust.
You have my dearest condolences and if you wish to take this to the PM stage, do feel free and I will gladly talk about it. But listen to a like-minded scarred veteran; Don't take her back. You will only break yourself in the end by doing so.
I hope you feel better in the morning - Otherwise, I'm sure a lot of people here are here for you.