Assistance?

So I've come to realize that I need some advice.

It's because, on monday I found out that my boyfriend of for months--and best friend of two years--is cheating on me with a friend of mine. When I went to his house to talk to him about it, it ended up with us both screaming, and me crying, and he was begging for me to give him another chance.

Now, I don't want to be that girl, the one who forgives a boy for cheating on her, but at the same time, Andrew and I have ties that run really deep. When we broke up the first time, we immediatly got back together again, like we couldn't funtion without one another. What he did though was wrong, and it hurts me just to think about it. Today I'm going over to his house to see him again and I find myself wondering if I should break up with him or not?

The thing is, he could cheat again, but on the other side, maybe he won't. I'm not so sure what to do and I feel really stuck. It is really horrible of him to cheat on me with my friend, but am I overreacting? Do I take him back or should I walk away now?

With love,
Emily.