Why do I feel like this after one date?

I realize this sounds very strange, but I'm hoping someone here can help me as I'm not sure what I'm doing anymore?

I met this girl online, we had everything in common, liked the same things, everything seemed perfect. We talked for a few weeks, non stop and then went on a date, had a great time and hung out a few times after that. For some reason though, she's decided she's not interested in me, which - usually wouldn't mean anything to me, I would simply go OK, and move on.

This girl though is completely different. It's been about a month since I realized she's not into me and I think she's involved with someone else now, but I can't stop thinking about her. It's making me depressed and causing problems in my work and social life. I haven't done any real work in almost a month because I'm so depressed.

I find myself going through her Facebook profile and upsetting myself more on a daily basis. I'm not sure what's going on. Apart from girls I've had a long involvement with, I've never felt anything close to this. What's going on with me? Does anyone have advice on how I can fix it? I feel ridiculous as I only knew her for a month before she decided that she wasn't interested, but she was just so perfect....

How long was it that you were seeing her?

Shes not interested and shes involved in someone else, so all you can do is move on. Delete her on all your social media sites. Stalking her on fb, instagram, etc, is going to do nothing but bring you down..