You found out about your wife's affair in February. Why would you have plunked down that kind of money for a trip a few weeks ago, when your wife was still in the thick of her waywardness?
I'm really sorry you're going thru this. This stage you are at right now is exactly why I try to get people to attack their cheating spouse's affairs EARLY and AGGRESSIVELY. Because when they are left "Bo-Peep," they usually just keep planning their own escape from the marriage, and the end is NEVER pretty. Financially, emotionally, legally, it gets ugly and very sad.
Dan, you've been stuck on defense far too long. There are some things you can do still, at least to minimize the damage. You need to take back some control in this situation! Sadly, your wife does NOT have your family's best interests at heart right now, nor your marriage's. The agenda needs to be set by someone who DOES, and that would be YOU.