From your post, I think you are a classic case of being introverted. I was, I found an article stating different ways to change my ways towards "extrovert" and I must say, it helped me out TONS when I felt alone and was severely depressed. Life is still a challenge, but I feel hopeful instead of hopeless.
Now, the first part of your post was worrisome, I am hesitant to comment because I hope I didn't take it in the wrong way. So all I'll say is that you do not have to change who you are, but relationships come in all different shapes and sizes. Though people may not share the same views as you don't put a wall up and hide, or cut yourself off. Give people a chance, and don't write them off because of their behavior. I have plenty of people that I converse with, just at work, and its nice to have those relationships.
Next, find a hobby. Join a bowling league, go out and sing at open mic's, take an art class or go to a gallery, take karate, join a walking club or runa marathon, anything that sparks your interest or a passion, just try it out! Life is to short to be living indoors. Besides its WAY better then a therapist, and usually more affordable. Not only will you will meet people this way, but you will learn more and more about yourself. If you are anything like me you will say "Oh, I've always wanted to try...." and then tell yourself, you can't. If you hear the words "I can't" then go for it. You will get no where if you don't push your boundaries, you will be stuck and still. If money is an issue, have faith. Remember, hopeful, not hopeless.
A couple of last things. Smile, even if its a stranger, you will make their day better. Make it a point to have a conversation (even in passing) with someone everyday, speaking just a little bit makes it easier. This was the hardest one for me, but saying "good morning" began cracking my "quiet one" syndrome. Keep your eyes up and forward, do not walk looking down. Body language goes far, arms open, eyes level, and a beautiful smile. Wear colors. And challenge yourself. What would you attempt to do if you knew you could not fail?