Marriage infidelity sucks. I know as it affected our relationship. It was really hard to stay with her - even though it wasn't sexual, it was still emotional and I still believe would have gone to sexual.
Anyway, we stayed together. It's hard, because I adore her.
Now, to all the people saying leave the bitch and beat her, toss her aside, etc. Until you have been through it, you can't even pretend to understand. Advice is welcome. Needed. But "leave the cheating whore" is too simple and wrong. In a case with children (like my relationship) it is impossible to to judge. Eight years? No. "Leave" is not the answer yet.
Finding answers, evidence, understanding - those are answers. If you don't get those answers you need, then you leave. If you can't find closure with her after truly trying, you find closure without her.
And yeah, everything is fair game, but honesty is best first. Then be sneaky. They always... ALWAYS slip up.