Neither, you should never be with somebody simply because you feel obligated. It is unfair to both him/her and yourself. I once know a girl who stay with a guy because she feel obligated and to make matter worse, she is in love with another guy. Fortunetly the other guy have a principle of not stealing girl friends, because he was really into her too. But even so, if you are that girl's boy friend, how would you feel, knowing all these. Or just know your girl friend doesn't love you at all. It is like finding out your wife is really a lesbian who never loved you, ouch.