I did something terrible: I cheated on my girlfriend.
I assume you feel bad about it?
Yes, I'm horrible for cheating on my girlfriend
I can see you are remorseful about the situation. It is wrong to cheat on someone. I'm glad you know that what you did was wrong and that you will change your ways going forward.
I was trying to make her believe it's her fault for leaving me alone with her best friend...
So you made it even worse by trying to turn it around on her. You need to apologize ASAP.