My advice is confront as soon as possible. There is no advantage in waiting. You have all the confirmation you need. By tomorrow you will have physical proof anyway. She was caught no matter if you got the call or not. Exposing the affair takes away a very good measure of the fun. He will probably start backing off, and she will have to weigh her options.
Trent is right. She got caught with her pants down (so to speak) but you have admitted that you could have been a better husband too. That doesn't excuse the behavior, but no one is perfect.
