It's an illusion, they ain't as they close as you think they are. Your mind's playing tricks on you. I used to be like that 3-4 years ago, but at one point I realised that complaining/trying to get external help is useless! I threw myself in with them, and now I can safely say I know the majority of my year, and on good terms, with occasional talks with some, and more often with others, go out with some of them as well at certain times, and all that came from just a building of courage to enter than illusion and make it reality. Believe, there is no other advice than to immerse yourself with the others, if it's awkward at first, persist and you'll understand what i've said above!
Good luck!