Just when we start to believe he is in love with Penny, he dumps her. And when we learn to trust him, he betrays our protagonist. When there is infighting amongst the band members, the emotion is real, even when it is immeasurably petty. Like real fighting amongst real people. It's frustrating to watch Hammond trade Penny to another band in a card game, but that's the point.
Love can be frustrating.
That's what people do. But by the time the characters disappoint us, as they do, Crowe has already made us care about them, so we are frustrated and disappointed with them just like they are with each other. And when you love someone, you stick around, hoping that they will eventually change their ways and do the right thing. Hudson may or may not be or become a great actress, but for this moment she is dead on as the object of everyone's affections. They are the ultimate fans, muse to the bands they follow and love.