Has anyone on here ever experienced this?

Last year, I started having dreams about an old friend who I used to hang around with about 5 years ago and was a nasty and spiteful woman but very good looking, and started geing obsessed with her by starting recalling all the memories with her in that kind of nostalgic atmosphere, then the obsessions built up to the point where it was intervening into my daily life, I suppose in a way its limerence, so, I started to forget about her on purpose before these obsession get really out of hand, then about 4 or 5 days later when I had the biggest coincidence in my life, she actually turned up on my doorstep totally out of the blue and there is me thinking well after all this time she would be a changed person so I thought I will give it a try. I did, and she has not changed at all, she still had her spiteful ways, so I broke friends with her again. So I tryed to forget about her, and couldnt succeed and as for the fact that the shock of it triggered off the fascination of the fact that you absolutely cannot believe you saw her, and started to get even more and more obsessed and now (6 months later) it has got to the point where it constantly, every second it pops up in my head about her (and it can be VERY persistant and graphic) and I have tried everything! I have tried to replace it with another obsession, that doesnt work, I have tried to overwrite the obsession with storybooks, that doesnt work infact when I actually get INTO the storybook, my mind wonders and it recalls all the things me and that woman have done in the past, I tense up my head and squinch my eyes everytime a pop-up creeps up to try and block it, and when I DO start forgetting, I get so far then I start having dreams about her (and BOY can them dreams be of graphic detail and the feelings in them dreams can really linger too!) and brings it all back up again. Also, when your trying to look at other things in the past, all I can literally see is her as if all my life I have done nothing BUT hang around with her. My goal is to forget about her and I feel that I am in a no-win situation, I really wish to absolutely forget her, but it is like a virus breeding in my head, and it feels impossible TO forget. What do I do? Is there a particular word to describe this type of obsession.