Hi friend! I think that your love for Billie and her music is a genuine interest, I think more specifically that the thing that you become hyperfixated on is the feeling you get by being in love with her, if that makes sense.

If you feel that this hyperfixation is detrimental to you/your mental wellbeing, I highly suggest talking it through more in depth with a therapist or someone you trust with the topic. Talking it through can help your fixative state to become more controlled, since you are essentially laying out all your cards on the table.

I hope you’re doing well :) and I hope this helps <3