Is it normal to keep thinking of a girl all the time, ive only seen a few times

so on april 2011 i accidentally met a girl while being drunk with my friends. it was quite funny. i told her my facebook name but i didn't even expected her to invite me as a friend. so we had some chats, i guess we both were bored. we kept chatting through the whole summer. in the middle of july i noticed i was developing feelings for her. all of our conversations were on the phone, and we met only once in the summer for a short time. idk why she didn't want to meet me, but she chatted with me like i was one of her best friends. and then, on october, it all suddenly stopped - all she ever replied was only a few words, she stopped starting conversations, for some reason she even banned me out of her friendlist on facebook, leaving me in the middle of a huge storm of confusion. my feelings for her froze and don't ever come down. now until now, i'm depressed about how unreachable she is. also i've lost her number. all i ever do is just think about her - the girl, i fell in love with on the phone. it's depressing. everything that surrounds me reminds me of her, luckilly i saved some of her facebook photos on my pc, i could stare at them for hours.

some facts that might help:
i used to take antidepressants earlier
i'm 18
i'm a very sensitive person
i have OCD

now i don't want any relationship advice, or guesses about why she did this. i know she's unreachable, i have to close the door behind me, but i just can't.

so tell me, is it normal to keep thinking about her every day for more than a year now? and how do i stop it?