My best friend had sex with my really close best friend?

My friend, who has been turning into a dick lately, told me that he nailed some chick that graduated 2 years before us and that was his 4th lay. I knew his first, and that last one was his fourth (obviously) but I couldn't piece together who the 2nd and 3rd was. Then it dawned on me. The girl I was interested in (but can't do **** because she views us as twins) was the one. I didn't want to believe it, but when she told me about the sexual encounters, I could barely contain myself. I felt a mixture of pure anger, complete and utter sadness and true disgust. Having that picture of them together like that, I was on the verge of tears. And she wasn't doing any better because she felt as though she truly "loved" him. But he doesn't give a rats ***. Pussy to him is like candy, you have one, throw it away and have another. But I can't let this go because she is the closest thing to me as a person, more than family. I'm going to hang out with him tomorrow, what should I do? How should I handle this? Do I just have a little chat with him, mano-a-mano? Or do I just give him everything I got?