My husband recently revealed to me that he slept with his ex wife when he traveld to Texas to pick up their kids for the summer. Now I know that the good Dr says you should cut off all contact with your lover, but how would he do that with his ex wife? She will be moving back to our home state of Colorado in a year or so...but for the next year she is still going to be in Texas while the children are here in Colorado with her mother. He has to talk to her...so how do we work around it. I have made it VERY clear he is NEVER EVER EVER to be alone with her again...if I can't go with him to meet her to pick up the kids then he doesn't pick them up. I honestly don't believe if it had been anyone else that he would have done it. And I also believe that she came on to him and did it out of spite to me...she has expressed numerous times to me that he was "terrible in bed and she hated him and didn't want him" which could all be a smoke screen...but I doubt it. So please give me some advice.

I agree with you 100% that your H should never again find himself alone with his ex-W and yes it is very possible that she did instigate the sex in order to spite you, but of greater importance is why your H could not say no to her?

so how do we work around it. I have made it VERY clear he is NEVER EVER EVER to be alone with her again
That is how you do it.