How do I get over a broken heart? He cheated on me with best friend (his, not mine). Sick.

Counseling, group Rx. Doctors, like psychiatrists, can provide counseling on issues like this. Self-help groups, and supervised group therapy might also help.
Look ahead. We all experience failed relationships and they hurt. And there is no understanding human behavior, especially when it comes to loving. He wasn't the right man for you. Work hard to be the best person you can -- here's where we can all benefit from professional guidance -- and probably you'll meet someone you can be with on terms acceptable to you. Good luck.