My best friend is really making me angry..?

There is no way to get threw to my best friend and its really really frustrating me. He is dating this really nasty sl*t and when i try to tell him he just ignores me. He says he doesn't care what i think, and this girl he is dating gave me a ******** like 3 days before they started going out and he knows that. She is really a huge skank... and i get so frusturated i get angry at my friend and I called him some hurtful things the other day. Does anyone have any advice what to do in this situation.. btw my friend is me for this nasty b*tch and its just confusing the hell out of me. He told me he really likes her or something. WHAT CAN I DO