Been there and done it. Tracked my W - didn't go to a kids party went to another man's house. Sex or not - I still don't know - she definitely had an EA (3 months). Your W will have a long track of communicating with this guy face to face, text, FB etc. It's just a fact. You don't need to know anymore. I am so sorry this has happened. It's nothing you did - so drop all that straight away. You will see over time that H's and W's on this board have pretty much all seen this. Experienced the same - almost exactly. Why? Something clicks in the WS. They are unhappy with the M. They are having a MLC. They just feel they are resigned to the scrapheap of life etc. Nobody can fully tell you because even the WS never fully knows (read Sandi2's posts for the best insight - she puts it down to disrespect in part - so don't allow her to do that, Sandi's info helps here). Try not to work out why etc. Try to get used to "it's not you, it's her". It is. She has a circus going on - don't get involved. Her Circus, Her Monkeys.
You are for now a one parent family. Become the best Dad and the best version of you. Nothing else. Expect nothing from your W. Expect lies and manipulation. Rise above it all. Don't get sucked into any emotional rollercoaster stuff. Just keep your mouth shut, learn validation and avoid all fights. Also, don't talk to anyone about this sitch. unless you are 100% sure it can't get back to her.
Detach emotionally, start doing things and ignore what she is up to as much as you can. Get out and start living your life for you and kids, don't talk to her about the R, OM etc. Don't ask for family time. Just be a one parent family.
There is lots of advice on here and in DB & DR. Time to get reading. Try to loose the fear. That's the main thing. Exercise is very good for this. Drinking is not.
Time to focus.
We will all keep checking in on your. Try to 'journal' - just like keeping a diary. It's safe to do so here. It gets things out in the open and you will get educated and unbiased help.
It will all be okay, even if the relationship does not become a blossoming M. I promise.
You are not alone. We have all been there.
Surfer.
M46/W40/D8/S6/T20/M12/Separated 6/2016,W takes kids Issues2009 Wpartying w/g.f's2013on EA2013PAdeniedWleavesMBR ImeetAP/EAhalts VariousBDDates MFCourse WSpew EAresumes I halt Wrages DBIng4/2016