I was more or less the same way. I don't think I fought with fans over any other series but Buffy. I even fought with fans over the Buffy comics - and I was a long-term serial comic book fan dating back to the 1980s, but I never fought with fans over the X-men or any of the others. Although, admittedly there was no internet back then - and I didn't have access to fan conventions.
Although I did interact with fellow comic book fans in college (that was actually how I got hooked - in college), but we never fought over it quite as passionately as we did Buffy.

No, Buffy was the only tv series I ever obsessed over in that way as well.