Upside, I think if you don't want to spend time with H's friend, don't go. I definitely wouldn't want my one weekend in months away with H to be shared with someone I'm not keen about! With any luck, there will be another time for you to get away with H. Of course you will want to thank your H for the invite regardless.
That's my 2 cents' worth!
Peace, Dawn
Me 45/H 47, no kids Together since 1985; M/1992 Bomb1 (EA-OW1, age 22) 2001 Bomb2 (EA/PA-OW2, age 22) 10/2007, A continues H left 11/24/08 minimal contact, no legal action http://tinyurl.com/DawnHope1