Re Lighting this thread, rather then having to tell the whole sorry tale again!, now be warned this could be long...
So I took him back..
I was pressured by my family (and of course him). Neither of us went for sti testing.
For a while all was good, improving (head in sand, I know!)
Starting getting depressed again (have history of this) back on antidepressants and they have really helped. I'm looking after myself much better, enjoying my DCs more. Not sure if if it's the meds but I removed head from sand and thought I need to deal with this once and for all. Started by looking at his emails. Found he had been sent some naked pictures from a lady (sent from an iPhone with a normal email adress, so not some spammy porn site) and some emails between them a little flirty nothing more. But this was happening while I was out for a meal with my mum.
So I went for an sti test just over a week ago (no results yet)
I got hold of the phone overnight a few days later. He deletes EVERYTHING! But thanks to the wonder of spotlight search, I found more evidence (I'll give you the edited version or we will be here all day) There was talk with the previous woman about christening his new car, evidence they met up to go the cinema (and said they prob wouldn't see much of the film) and her mentioning it had been going on for over a year. He had also sent her a picture of our newborn DD 
Also lots of messages to numbers (no names), which show arranging meeting up, including asking if she wanted his wedding ring on or off? (which she said it wasn't his wedding ring she would be looking at).with one he was asked why he stayed with me and he said for the kids and money reasons.
Unfortunately with spotlight I don't know when these messages were sent (before or after last time I found out) or who said what.
Last night I also found him on a dating website. Not much on there but his profile pic is a selfie is taken in our bedroom and you can see the canvas of DS as a baby in the background 
So that's it, I'm done. I'm kicking his lying, cheating arse out (I don't care if it is nearly Christmas). I'm almost looking forward to it.
My plan is to get sti results first (may aswell have all my evidence) and also I'm working this weekend (my only shift this month) and I will be needing the money come January, so I may aswell hold fire (I will be sleeping at work, only home for a few hours each day).
Hope to have results By Monday/Tuesday, then I'm doing it.
Was thin king of saying I've had the results and I'm now going to ask him one last time if he's slept with anyone else.... (what do you think?)
I almost want sti results to show something, but think I will bluff even if they don't ?
Any advice/hand holding is so appreciated as I haven't told anyone in RL x