H left about three months ago. Changes relationship to single on FB two weeks after tellling kids (upset them a little, my S was sarcastic as h*ll in his reply lol!)
Was sleeping with someone else by that time I am sure, but continued to lie to me for another 6 weeks until I called him out on it.
For me, it is also the lying that is the dealbreaker more than the sex. That I understand because ML in our R had been crappy for a while.
H has also always been a liar, mostly to himself, I think, about justifications, and actions etc. I just never thought he would lie to me when I asked a direct question..and he did repeatedly.
Funnily enough, his issue with me is trust, never mind mine with him.
I also said that our private lives should remain private-he tried to friend me (after blocking my butt) on FB several times and I said "no". This was to protect me from allowing the hamsters to start running in my head about pictures, etc. And I would obsess too much. So it is a good thing that you blocked his feed.
What really bothers me is the comment "BTW, you're not getting the kids back..." Do you guys have an agreement? Maybe it is time to see a mediator about that one.