My friend is dating my ex-boyfriend?

My best friend in the whole world that i've known for two years is now dating my Ex-Boyfriend and it really bothers me. She just told me yesterday and I am still in love with him, I started crying my eyes out and she just said "Oh, you'll get over it! What's up?" She didn't even care that I was upset. I wish that she could fathom the pain and betrayal I felt last night. So should I tell her i'm happy for her and suck up the pain. Or that I have to just move on and tell her we will no longer be friends. Someone please help me, i'm very confused and upset right now.