fan crush

a quickly formed (nearly instant) adoration for someone of the opposite sex, based purely on a shared interest/obsession. Be it a sports team, band, tv show or hobby. Often confused with a crush at first but this intense feeling fades as you get to know more about the other person

Steve: Mike has been talking about that girl Beth ever since he found out she loves football as much as he does
Jessica: That fan crush will be over as soon as he finds out she hates his favorite team!