Why do I hate people so much???????????

I hate being around people. I'm happy when I'm by myself. I'm unhappy when I'm around people. I'm 19. A normal day for me is real simple. I wake up, & go to school: college that is. I get home & go to my private gym. I do weights, boxing, & cardio. Then I go eat. I come back home to study. Then the rest of the day, I either watch movies, read, play the Xbox, play on my laptop, listen to music, or go for a drive. I have no friends. I've never had one friend. I've never had a girlfriend. I hate being around people. I do help my grandfather out a lot. He's really the only human being I talk to. lol. I still live with my dad, but we don't get along. I hate my stepmom. I don't ever see my real mom. She left me when I was 7. I got bullied in grade school & junior high. Highschool was ok. A lot of people wanted to be my friend in highschool, but I stayed isolated from everyone. I don't ever want friends. I don't ever want to get married. I just want to live by myself forever. People say that I'm weird & that I'm depressed. Why am I like this?