So sorry justnumb. I know you are obsessed with this thought and there will be more. The problem right now isnt' her. It's your H. The person you are supposed to trust more then anyone has betrayed you - again.
I see that you have kids too. You need to take care of yourself so you can take care of them.
Your #1 demand - not request - demand is that he goes NC with her. Immediately. Have him write a NC letter. You need to see it.
Your #2 demand is that he answer all your questions and write out a time line of when this started, where it happened, etc. If he does not, he can leave. In fact, you can tell him to leave now or anytime. Get your "bitch boots" on until further notice!
I know. This is not what you want but you need to take a very hard and direct approach with him right now and this time around.
Your #3 demand is that he gets himself into IC. Forget MC at this point. That will only work if you have a partner who is willing to own his behavior and start behaving like a man. He needs help. You need help too. I would recommend IC for you too.
This shit is hard enough and I cannot imagine doing it w/o help.
Justinpaintoday is new too and I have some seen amazing growth from him. Take his suggestion about reading from the Healing Library. Knowledge is power.
Hugs to you.