Because she already almost died once. She can't react the proper way when he get hurts and that dumbass only push her away again and again. He was so busy being miserable that he didn't see that she was getting tired, sick, stressed and that everyone around her is agaisn't her. He just ''found out'' when the mother yelled at him. That's not a healthy relationship at all.
They should work on both side on their competence and then try it out once more. But until the guy stop complaining that the whole world is agaisn't him and forget about her feeling too in the process and the lady start learning proper paraplegic care. It will happen again and again.
I think she should break up with him. Work on herself physically and mentally. Or even take medical course to learn to take are of disabled peopl, stay friend if its possible and see what else the world can offer. She almost killed herself to take care of that dude. And all he do is crying on how despicable he is. He never saw how she was and only tried to distance himself, over and over.