That happened to me earlier this year. What made it even worse, he kept telling me to break up with him, how my boyfriend was an awful person and that he had no respect for him.
I break up with my boyfriend, and then one week later, my friend started dating him. The worst part is, he was my manager at work and had to work with him everyday while trying to act professional around him. I cried in the backroom a few times, especially after he told me "I'm sorry that you're hurt, but I'm not sorry for taking your ex". Nine months later, they are still dating, and I'm cool with both of them, but I'll never forget what my "friend" did to me. I never viewed him the same ever again. If he needs something down the road years from now, how he treated me will always stay in the back of my mind.