Girlfriend Cheats with My Best Friend - Ever Happen to You?

Has anyone else ever experienced a situation where your best friend has cheated on you with your girlfriend?   It has recently happened to me and I am having a hard time with it. Would love to hear from others?  I thought maybe it might help to make some sense of things or what people have done that has helped you process it and move forward? I have never felt so betrayed..and the worst part is I have to see the 2 of them in a particular situation so its like in my face. 

Anyway, would love to hear from any others?