Single, Lonely, Depressed, and I just don't know why

So I've been single my whole life, about eighteen years, and it's certainly not been fun. But to make things worse I have depression.
I always seem to hit it off with a girl and things seem great and it seems like she likes me and I like her so all seems good and well. Then I'll ask her out or even stop and tell her how much I care about her, and nothing. She looks at me like I'm a nutter, that whole, "Wait, eww, you expected me to like you?" Completely shot down and denied. The thing in itself seems odd looking at it from societal point of views; I'm handsome(or so I've been told), I'm smart, I don't smoke or get drunk, I've got a world of possibilities before me. Even from the personal(I'm not sure what phrase to use there, like a good personality and all)view; I'm compassionate, I care, I'm a Christian man, I seem like a good person. But no matter what I have never had a single girl who likes me. No one has shown any interest at all, most of the times they just ignore me or push me aside even after they seemed to be into me for so long. No one has shown the slightest care. Ever.
And it hurts.
I constantly wonder if maybe there's really something wrong with me that people hate. Something I can't see and no one will tell me about. Which with the thought adds to the depression I already suffer from due to other issues and I find myself in a really dark place where I wonder why no one cares about me at all and if it would just be better for me if I went away or ended it because it wouldn't have any affect on anyone else and it'd at least end my pain. Pain coming from the idea that I'm always going to be alone in life, like I won't ever find the girl I love, who loves me. Feels like my chest is going to cave in and I can barely breathe because I feel like there's never going to be anyone there for me. Something in my stomach trying to claw it's way out.