This happens to me all the time! It's actually kind of unprecedented for me to stay so into a fandom/pairing for more than about nine months or so. I still like them and read the occasional fic, but my obsessive passion for it usually fades. But I got into Buffy over two years ago, and it is going nowhere. Sometimes I think it will, but then I see a gif, or I'll hear some song that I associate with them and then I ship them SO HARD I just want to punch something.