Hope, I'm sorry you found the panties because like you said no matter what his explanation it isn't going to be enough.
I remember going through it when my W cheated, I was so naive. I believed all of the crap, until everything finally came crashing down.
I cannot understand how people (both men and woman) cheat? I almost 34 and I've only ever had sex with my W. Sure I've had temptations in the past but I never came close to cheating - I just never would, it's not in me.
Bottom line is though, you need to understand whether this is a deal breaker for you (assuming you confirm it) or if it's just another thing to work through because you want to be with your H regardless of the mistakes (big or small).
I hate everytime I read on here about who has been cheated on or suspects cheating - it brings back horrible memories.
I feel really bad for you Hope, but only you can determine how you will deal with it.
Good Luck! Thinking of you.
BITS SIC
Me - 34 W - 33 M - 8 years T - 15 years D7, D5, D2 Bomb Nov 10/2010 "I'm not happy and INILWY" W Staying for the kids Mar 13/2011