[absingleman]

OP

In my opinion, I don't think this guy enjoys having sex behind his girlfriend's back. The only way to get him to join you without getting him drunk would be to have a talk with his girlfriend, then have her tell him that she would be alright with him playing with the two of you. Of course, she will probably look for a couple of her own to play with, and that might not go well with him.

Other than that, give it up. You had one threesome with him and he hasn't brought it up or tried to initiate it again? He hasn't tried to hit on your girlfriend behind your back? He hasn't asked you if you wanted to do it again? He watches porn with you but doesn't even look like he wants to do more?

Guess what. He doesn't want to repeat the experience. Maybe he felt guilty and told his girlfriend and she threatened to break up with him if it happened again. Maybe he felt guilty and is afraid to say anything because she would break up with him. Maybe sex with his girlfriend is better to him than sex with your girlfriend. Whatever the reason, he doesn't want another threesome with you. Everyone is entitled to try something once. That doesn't mean they have to like it because you like it and they have a lot in common with you.

Don't push him on the threesome thing anymore. And when you go on this trip, make sure you have seperate beds. One for you and your girl, and one for him. Better if you can get seperate rooms or can get his girlfriend to join you somehomw.