Ulquiorra felt the seven deadly sins towards Orihime, and those sins are all emotions. He has become envious, hunger (great desire in this case), lustful, prideful, lazy, and angry because of the heart topic, which slowly made him want to have her all to himself. With all of those emotions going round in round inside him, Ulquiorra has become a hollow that is confused and doesn't know what to do at all since he doesn't remember what these emotions are. You know what happens when people go through a lot? They go insane, right? That's what Ulquiorra was acting like from the moment he was told...