Major obsessions I had (in the order they happened): animals (I think, can't remember the level of obsession), reading, ancient Rome, Nik Kershaw, internet chatting, learning English, guys I liked, Asian TV series, learning Korean, volunteer work that benefits people who aren't treated fairly by society (not sure if this one counts as an obsession, but I do get pretty intense)
Plus many minor ones who stayed for a month at a time or so and then just faded away: playing guitar, playing piano, playing accordion, psychology (recurring), drawing, writing postcards, learning Persian and many others