Don't know if this would help you - but here is what happened to me:
About a year and a half ago, my DH's FB page was open. I have no idea why, but I clicked on his inbox, and saw that a few months earlier her had made arrangements to go to drinks with a 19 year old that he met at a festival.
He was going to meet her in manchester (he was there on business) - he hates driving in cities where he has to find places. His family lives up there and he could have spent the evening with various relatives who he loves and gets along with. This happened at a time when I thought we were solid as a rock. I had fallen in love with him again. He told me that he was going out with a male co-worker. He DIDN't end up going as work got very busy and prevented him from going.
SO, when I found out, I tried to play mind games about it - I woke up the day after I saw the email (I was very detached about it after I saw it as well) and I was very upset. I said " I had a dream that you made plans to go out for drinks with some 19 year old"
He looked me in the eye with warmth and love and said "why would I ever do that when I have you?" Then he laughed and put his arms around me.
If I hadn't SEEN the proof, I never would have doubted him.
Get proof.
By the way - I NEVER in a million years would have thought that he would have done this to me. Never.
He moved out a few months ago - after a year of me doing everything I could to fix things. I wanted to be able to look at my kids and know that I had done everything I could to save our marriage.
Good luck darlin