Being a loner ain't all that bad.
I prefer to be alone, but it doesn't bother me either way.
I'm a pretty chill dude when it comes to people, or anything really.
Anyways, depending on your age, it could be plenty of reasons.
If you feel it's really affecting your life and you just don't want to live that kind of life, ask a parent or gaurdian to get you a pyschologist/therapist to help you out.
Other than that, that's all I can tell you for right now.
Good Luck man, send me a pm if you'd like a little more help