OP here. Three months have passed since >>1, maybe it helped me put some things into perspective... I'm not sure.
What happened later was - I agreed to "stay friends" with her as I didn't want to lose her completely. However, this didn't work out well. I was feeling extremely happy while taking to her, just because I was able to talk to her - and unbelievably sad every time we said goodbye, because I knew there was nothing for me to look forward to.
(I wrote a bit about it there, I'm OP of the "to get over?" thread if you want to look for it.)
After two months of that torture I finally brought myself to "cut her off". I wrote her a very long letter, describing exactly how I feel and how devastated I was feeling (I know it was a quite selfish thing to do, but I still wanted to let her know) and asked her not to talk with me again for some time. She understood.
I think I did the right thing. What was happening with me was only becoming worse. (I really don't want to become like >>17, "masturbating to fantasies of torturing and killing her", I also don't want to get suicidal, which may or may not be possible for me; and most of all I don't want to bother her anymore with my feelings - that letter should be the last thing I ever said to her about that.)
What I did was basically getting rid of the "feeling extremely happy while taking to her" part so that I can get used to the sadness. I still think about her most of the time - there's no way I could forget in just a few months - and I still have fantasies of her changing her mind (can't do anything about them...the slightest hope of her liking me was what kept me going for all this time, it isn't easy to kill - would there be a method for that?) - but I hope it will all fade away if I wait. I don't know for how long do I have to wait, though - some more months? Half a year? Years?...
(I don't think I will fall in love again anytime soon. You have to actually know some girls in the first place... And it sucks that when you act openly and don't try to hide your commitment, you're most likely to be viewed as a "nice guy" and "a friend".)