Like others have said, nowadays stan is someone that’s more involved with whom ever (by spending either time or money devoted on that group by keeping up with their content and supporting them as they can.)
Fan is a bit more casual about it, but still keeping up here and there. And keeping track of their songs somewhat regularly.
I don't consider myself a stan or a fan(atic) of artists or groups. I am a fanatic of music especially if it's quality songs and albums. That's what I enjoy supporting.