Lost, I think the Hawaii trip may just be the thing that is your opportunity to tell the kids EXACTLY what is going on. They deserve to know the TRUTH. And not some spin that your W will try to give them.
I agree with this, Lost. "Your mother has a boyfriend, and it's not right for married people to have boyfriends or girlfriends while they are still married. I don't agree with it, and I've asked her to stop, and she refuses, so that's why I'm angry, and that's why you've had to hear some of the disagreements you've heard. I'm sorry -- this is NOT your fault. I still love your mother, very much, but this is a choice she is making, and I obviously don't agree with it. And I can't just pretend it's okay and go on vacation with her while she has a boyfriend -- it's not right. I'm sorry, but this is her decision to do this, not mine."