Don't worry ~ you won't be the only gay guys on the ship. Look for the FOD (Friends of Dorothy / Rainbow Get Together in the Patter (usually the first sea day).
Our last cruise aboard the Grand Princess (October 2003) there were 6 male couples and we all became really good friends. The guy who hosts the party/get together is named Lawrence. He's one of the performers on the ship. He said that most trips there are usually 20-25 people who attend the party.
Have fun and enjoy your cruise.
Oh yeah, and one last thing... don't miss the opportunity to have your photos taken on formal night. It's a perfect time to get you pic taken as a couple and the photographers are more than willing to help you get the perfect shot!
Todd & Jeff