If you say he acts kinda shy around you, then the mates are there as a comfort net basically, if conversation with you goes stale, he can continue the evening with his mates or get them involved with your conversation.
As you state, he spent most of the evening chatting to you, when his mates were with you, which is some kind of sign to me, that he's interested in you.
Maybe next time, go for the meal out at a nice restaurant. You can learn a lot about a person from that, according to my girlfriend ie what type of restaurant they take you too harvester, italian, french mc donalds etc whether he picks you up in his car, whether they pay for the whole thing, and how they end the evening.