Die-hard

From Cambridge:
diehard, die-hard   Show phonetics
noun DISAPPROVING

someone who is unwilling to change or give up their ideas or ways of behaving, even when there are good reasons to do so:
a diehard conservative/fan

A die-hard fan of a Philadelphia Eagles football team (for example) will continue to support his team, even though they are playing terribly this year.  A fair-weather fan only support his team when they are winning!

I don't necessarily think it's a disapproving term...as indicated above...actually it indicates you are a very loyal fan.