Girlfriend thinks I don't love her

This is actually my friend's problem. My friend, a guy, has a girlfriend who he loves loads and loads and who he'd do anything for (I'm the girl, his friend, who can also see this.) BUT sometimes she says he doesn't love her...she says he igores her. However, this really upsets him because he knows that he does love her and he doesn't know why she's think he doesn't. He's always with her 24/7 makes she she's happy and is nice and caring towards her etc etc.

I think she's emotionally blackmailing him, making him dependent upon her. But he doesn't think so. So, my question is, why would a girl say that her boyfriend doesn't love her when a) he truly and deeply does and b) it's obvious, through actions. How thoughtful he is and all the special things he does. So yeah, why would say say this?