I'm sorry you are here and I know how you feel. About 4 months ago I got our cell phone bill and it was thicker then usual. Our service provider AT&T provides detailed billing so all inbound/outbound/texts are displayed. Just the numbers and times are displayed and I'll tell you it was 100's of texts to a number (her boss). It was all hours of the day/night.
Long story short, I was able to confront her and find out she was having an EA. She has since then moved on from boss to other co-worker to have PA. Needless to say we weren't able to work things out and D is on the table.
I even went as far as installing a "Keylogger" on my PC. I've captured some interesting emails/chats to OM1 and OM2. I would certainly do your due diligence in finding out.
I hate that your in this position and I feel for you. The betrayel takes over but I'll tell you that it gets easier coping. I'm healing everyday from this and you will too. Good luck.
M: 36 W: 29 S: 2.5 EA: 2/2010 OM1 D Bomb: 3/2010 PA: 6/2010 OM2 W moved out 8/2010 Loc: DE, USA