I'm losing my mind because of my ex-girlfriend

My ex-girlfriend left me over a year ago. We were only together for 6 months. Nonetheless I still became very attached to her. She was my first girlfriend and I still haven't been with anybody else. She seemed so different from other women.

I've never suffered from anxiety before but until she left me. Nowadays I can't stop my chest from hurting because I'm so freaking distressed all the time.

Soon after we broke up I realized I became more and more obsessed with her. I didn't stalk her or anything, I just _always_ thought about her and couldn't let go.

The though of her seeing someone else was killing me and I thought things couldn't get any worse.

However I've recently discovered that my best friend has a sexual relationship with her. Yes, my best friend is screwing the girl of my dreams and the one I'm obsessed with. Words cannot describe how painful it is.
I've told my psychiatrist only a fraction of all the miserable things that has happened in my life and he says I suffer from severe depression. I wonder what he said if I really told him everything.
I've thought of getting a new girlfriend but I'm so depressed it's really not an option. However I think if I met someone new she would make me feel better and that would solve my problems.

But the thing is, I'm not really good at meeting new people, not to mention asking someone out.

I work somewhere where I meet a lot of new people everyday (way older than me though). From time to time people tell me stuff like I have a really good attitude and they'd like to know me better. Some people even compliment my physical appearance. My point is I don't think I'm a completely lost cause in the dating business.

I feel like online dating is my only option but I'm sooo bad at giving a good impression to someone by just sending them a message and coming out as interesting. Like I feel that girls in online dating websites get so many messages that I need to be somehow special to get their attention. I really really dislike the whole "hunting" scene in dating too. I don't want to chase after anybody.

I treat everyone very kindly and I'm always really helpful but I feel like all I get in return is ****. I don't think I deserved all this to happen to me.

I'm only hoping to get some sympathy from here and maybe even some advice on meeting new people. Thank you.