2. Don’t threaten the guy she cheated on you with: This is a bad move and might end up working against you, just showing how desperate you look.
4. Face her: When you do, let her know exactly what she did that hurt you. Tell her why it is so painful to you. She would grovel and apologize but you should be as succinct and direct as possible. Stand your ground and stick to whatever decision you have made concerning the issue.
5. Take time to heal: Accept that you are distraught by this. Stop questioning your ability and what you could do better or not. Know that regardless of whatever effort you put, she would have cheated, still.
Understand that there are a variety of reasons why she did this… some of which might have nothing to do with you.