Hi Seeker,
I am 110% with Kimmy and Fay on this one. Enduring this kind of emotional dynamic is what brings a lot of us here to PC in the first place!
This guy is 'dumping' on his wife and I wouldn't go near the trip with a twenty foot pole. If only there were some way to explain to your friend how you really feel, but this might make things worse all round. It's tricky.
Maybe you'll be able to say, very gently, that a 'girl's only' trip might be nice one day. I wouldn't worry about missing out on the rocks. I would rather eat rocks than be cooped up with that guy.
I think you folks can tell that I've had a dose of this scenario myself, as I don't usually get so excited in the forum. I hope I'm not projecting too much.
Cheers, (slightly triggered) M