Fantastic, Evian, I'm really glad it went well.
You're not actually going there with his mates in tow, but they are just going to be there - is that right? So you're not going to be spending the whole evening with them. I suspect he wants to show you off to his friends, but chances are he'll want to spend most of the time alone with you as he obviously likes you.
Tenrec's idea is good - why don't you make sure some of your friends will be there as well. So at least you can say 'Oh there's xxxxxxx, just going over to say hello, back in a minute,' if you start feeling too uncomfortable.
But I've got a feeling it will be a lovely evening. xx