Have you talked to your husband about your concerns? Use "I" statements, maybe something like "I'm worried about how I will behave when we don't have the kids around. I don't want to focus my sights on you and cause problems. Yet, I really want to go on this vacation with you and for us to have an enjoyable time......."

In the meantime, could you talk to your therapist on the phone for a few minutes about it? Is that allowed?

Otherwise, perhaps you could agree to spend some time apart during the vacation? (I don't know the details about it.) And even agree if things start heating up, either of you can just call a "time out" without getting mad about that. Take some books along. Do you possiby have other hobbies you could take along, too?

I hope these ideas might get you thinking about possibilities, anyway. It CAN be done, but I do think a "plan" needs to be put into place.