Well, i'll tell you what I know....
1 Dh had 2 pictures on his phone of a girl he went to school with. She had takedn the pics, posing in a mirror, in her underwear - posted them on Facebook.
2 Dh had a 'sexual encounter' (blowjob) with a girl he met on a job, he was texting her arranging to meet again when I found the messages.
3 He has deleted numbers from his phone and from his FB account since I have been digging for info
4 Dh was registered on a dating website. This hasn't been used since 2010, no pics on it, just general portfolio. No proof of any meets.
5 Photos received via email (4 occasions that I found) of 2 different older women naked.
6 He has been texting and messaging girls through fb and through meeting 1 or 2 through work.
This is only what I definitely know. There is probably (I'm assuming) more, but I can't find any evidence and he's not telling - not that I would believe anything he told me now anyway.
So no affair, but lots of secrets and doing things that IMO he shouldn't be doing.
I have asked him Why?, he said, he has just given in to the attention he has received and been too flirty. He says it was just an ego boost as I don't show him lots of attention and affection at home. In hindsight - he's probably right about that. You know how it can be when you've been together a while, take each other for granted, Dh working long hours, me being tired and busy with doing everything else and having the baby. For me it isn't an excuse, but it is a reason.
For those who don't know, he works for an energy company and is in and out of customers' houses all day. He is out right now. So he has the opportunity.
I have always trusted him completely and have never checked up on his e mails or phone etc. Tbh, I feel that I don't nag (I don't see the point), I sort / clean all the house, look after the children, sort out shopping and all the running around that comes with being a SAHM, I do all the 'wifey' and 'Mummy' duties. I'm fun, really placid, I'm not hard work, I'm easy going, in fact I'm quite a catch!! 
So it's not the worst type of betrayal IMO, but betrayed I am. And I don't feel I know everything.
And I've always thought that everyone deserves a second chance, but he has broken me and I feel I'm living with an utter stranger.
WWYD?
Run?
Work at it?