Ignore the affair.Having an angry you to fight against will just push them together. Instead work on being happy. Go out and do things just for you. Do a 180. Be pleasant and bubbly even around him, speak softly, listen to him, don't talk about yourself and never ever mention her. Don't forget, anger is your enemy.I did this and it worked. Statistically affairs last on average 6 months. This of how you will feel when you do reconcile.