Why can't I get along with people?

First of all NO don't isolate yourself. I am a bit younger at the age of 16 and have gone through somewhat of a similar experience as you have.. The friend telling me to go out more and blah blah blah.. the thing is we've been friends for about 5 years and for some reason I didn't care anymore. Our friendship was fading and I didn't want to talk to anyone I wanted to be alone. I had no desire to read anymore and I used to love reading .. I lost interest in many things. I eventually found myself happy when I was alone in my room with the blinds closed and just laying in my bed watching television. I cried for no reason and counted down days and hours until school was over or when the weekends would come or break or anything. Up until I realized I was counting the days till I died. That's when it hit me that something was wrong with me, I was depressed. It took me from November to October to barely realize it and the only reason was because I had isolated myself SO much. October was the worst month. 2009 was the worst year. I don't EVER want to go through that awful period of time ever again. I don't want anyone to go through that. I would get annoyed at the littlest things as well.. and I found everyone immature or plain annoying. I, too would ask myself, " Do I really want to act all fake and call someone I barely speak to a friend and in a couple of years when we graduate we'll most likely never see each other?" What's the point? just enjoy your life.. try to act like you're interested.. eventually you may find someone who you can genuinely like to talk to, and make a friend? Up until now I have gotten better, but I have to admit I still feel down a lot of the time.