I think he feel that it's his responsibility to take care of his parents, 'cause all the other brothers doesn't want to do it. I don't think you need to say that to a girl, you should put your life first before your parents, whatever happen after you married her, you'll deal it then. Some girls are understandable, they don't have problem living with in-law, but to put the question before starting a relationship, it feels like he already choosing his parents over you, and there will only be more problem.
And this is not my problem, a cousin is doing that and I told him, he will never find a wife.