I will try not to make this too long.
tonight while trying to install an app on DH tablet a FB message alert popped up from a woman whose name I recognised.
when I was 7 months pg with DD, DH had a work night out, got completely drunk, phoned me by mistake and I heard a lot of commotion in background and a woman telling him to 'get in the car'. when he came home I looked at his phone and there was a text from someone calling him babe. I text back saying whose no is this and reply was 'X' from earlier tonight.
next day I went ballistic. He said nothing happened and she was with a boyfriend. I let it go.
2 weeks later I find a receipt for a (quite expensive) lunch for 2. again, I went mad, he claimed he met her and her BF. He apparently ate nothing and the receipt was from their meal 
then a text arrived from OW along the lines of "thinking about u too. hope all is okay but if not would be great to see u"
I phoned OW and she backed the story up but said her BF was out and she'd get him to ring me when he came in.
He didn't and i got a text from her saying she wasn't getting involved in whatever domestic we seemed to he having.
DH swore nothing happened, i had no proof, I let it go even though I knew he was still texting her.
I found her FB page and basically stalked her for months
she was 4 or 5 mth pg when they met but was single. eventually I stopped looking but never forgot the incident.
fast forward 4 years to tonight when I find out he is her FB friend. He can't understand why I'm angry and upset. We argued and he got angry that I was talking about something that happened 4 years ago. again proclaimed his innocence. think he was shocked i knew a lot from my FB stalking. He deleted her off FB then said he was deleting FB altogether. said I didn't trust him, I'd ruined his evening etc and sat in silence all evening.
was I out of order?