I Dont Believe In Cheating

My girl "friend" kissed another boy when she was being in a relationship. Then she said her boyfriend that she regeted and they would break up. Her boyfriend was angry so much. However, after that, her boufriend forgive her. They came back, and they still together happily. It seems fiction, but it's truth. You can image, if they had started with someone esle, now will they be like that?
But I still think cheating can't be forgive. So, how do we know if our partner cheat on us? 1TopSpy can keep you informed about all the chats present on the target device: View all Facebook chat conversations; All Facebook chat conversations messages are uploaded to your online 1TopSpy control panel which you can access from anywhere with an internet connection; Get time and date stamps to know when each chat took place. You will know what your partner is doing.

No way I can see myself cheating, I'm in a wonderful relationship