It's a story about a woman desperately trying to have a loving relationship with a man who's incapable of that. She insists on a relationship with him, because she believes that she can transform him through love and sacrifice, and make him realise that he actually loves her. He warns her that he has nothing to give, but he still gets into a relationship with her for the comfort. It hints beautifully at the bizarre and dysfunctional ways they manage to connect and attach to each other, and the failure to go deeper. She gives him her all, but he still has nothing to give, and he even keeps hurting her. Still, she doesn't stop hoping that he will eventually heal, and only then he will realise that he loves her. This is the saddest part about it, because she can't accept the failure and give up, entrapping herself in this miserable situation. Unless she's a masochist, which is possible, because at no point does she raise any expectations and is always coming from a perspective of altruism, but that's equally sad too.
The moral of the story being: if somebody is in a deep dark place, showing them the light of love is not always enough to lure them out of there.
She sounds very much like somebody with a savior complex.