Mate being an ?

So i have known this dude for about 6 years and have been best mates all that time. Lately his been hanging out with new friends and been clubbing with them and i have been invited out with them twice now. Now for some reason he always seems to get weird in social situations. If theres more than 3 of us, he wont really talk and have a laugh with, in fact he just acts like a total childish moron. Anyways the second night he hardly spoke to me and on the way home he asked 5 people out of the group if they had a cigarette and they all said no sorry. And when i said no sorry cause i only had one left for myself, he threw a fit and said thats it your tight im not inviting you out again. He made me feel like a total mug and a tag along for coming out which im not cause i got my pride. Anywyas i found out he went out the other night with them and didnt invite me and im not going to go out with them again anyway. Whats going on? Dont want to loose him as a friend altogether but i told him he was bang out of order on facebook and he hasnt seen it yet. Acting like a mug? What would you do.