How should I handle this?

I have this friend who tends to flip flop on how he acts around me. He rarely responds to my texts, but he isn't the only one, He ignore 50% of facebook stuff, but doesn't ignore the stuff that would be expected, such as answering questions when i go back and say nvm. He will one day ignore me in cl, the next talk to me like we talk all the time. We used to be best friends, but lately he is hanging out with some friends, who have made it clear that they don't consider me a close friend. I created a facebook event today for something that he said in the past he wanted to do, yet he ignored the invite. I KNOW i invited him but now his name is nowhere to be found. anytime i try to ask him something over facebook, he usually ignores it, if i send him a text trying to organize something with a bunch of friends he ignores it What is his problem? does he not want to be friends anymore? if so, then why is he friendly when he is and slip back into the old best friends familiarity he does on occasion? What is going on and how do i handle it/ find out