Ok, I haven't read back to far. So I don't want to just jump the gun.
So you know a trigger for your husband was this male work friend, but you continued to go out with the guy? Was that a 180 of some kind? He'd ask you if you were with him, you'd keep it from him, but then you'd get to ask what the status of his "friend and him" were?
Its sounds like you both were playing a viscous cycle with each other, almost knowing it would hurt the other. I'm certainly not saying he's innocent in this by any means. But were you DB'n or him?
I'm not sure the concept of working on the marriage when neither of you can even be honest? Another question, why would you call him to ask him to watch the girls on a night that you already knew he was supposed to have them? Does he normally bail out on his nights with the girls?
ok ok, I need to read the sitch more I guess, some of this is very confusing for me.