In need of advice

Hi, the reason im posting this is for help understanding what is happening with my friend. In August a very good friend of both of ours was killed in an accident, that both of us ended up being at. My friend was actually the one that called 911, anyways a week after that we had gone to Vegas together and everything seemed normal until about the first weekend in October he went to homecoming where or friend had gone to school. I have known my friend simce he was in 7th grade and he has been like a little brother since he was in 8th grade and weve both said that. Ever since he went to homecoming at our friends who passed away school he has been different. I didnt hear from him for a month at all and then when i did, it was extremely different. I know hes hurting and its easy for me to see. But when he disappeared for that month he began hanging around some new people and now they are the only ones he hamgs around with. He just drinks with them and thats it. I have spoke to a few other people that have said he has done the same ro them as well, not talking anymore and not seeing them either. Anytime that i bring it up to him he wont talk back or will flip out and say nothings wrong. I guess im wondeimg if what hes doing is normal, by hanging out with new people and getting rid of old friends at a time like this or if he is just getting rid of us completely? He has told me more about how he feels than anyone else and i know him better than anyone so its really a difficult situation. Thanks for any advice!