I'm not sure I love my girlfriend as much anymore?

The last thing you want her to do is quit her career, but at the same time... She has to be balanced. Make more time for you. If you feel she is worth it, then find the best solution in which will make you both happy. Even if that requires more time for you. Have her take time off from the band and you two take off somewhere. If the sparks are still there then so is the love. If you feel nothing and empty after spending alone time with her, then the love has faded beyond repair. Love can be defined as many things and one of those things are "action". Actions such as sacrifice or doing things together that made you two fall in love in the first place. If she can sacrifice some things in order to love, you might see or feel something more. If you dont feel it will improve or work, you can move on knowing you gave it a try. She can move on and keep this as a lesson to learn from.