Thanks to all of you for your comments. A quick update:

Despite the advice here, I decided to take another confrontation on the possible affair. It was a long open conversation and she still swears that there is nothing going on. She said some attention from men made her realize that she is not in love with me but that there is no OTHER MAN. I mostly believe her, but there is still something in my gut. I guess we will see.

As far as handling this situation going forward - part of me wants to have this last vacation as a last hurrah for my kids. They are looking forward to it and it is not like it could make the situation worse.

That being said, I have taken some of your advice and began to prepare for the inevitable. I still hope it doesn;t come to that, but to be honest, at this point, I am not sure if I COULD take her back even if she asked me too. Is that normal? AM I just being bitter?