First off, no matter what the circumstance, what the son did is not acceptable.
However having seen a similar situation first hand, and in that case, although from an outsiders point of view, like this, the mother appears to be a saint by sacrificing everything for her only son, if you had to stay with that woman, she would drive you totally nuts.
So I feel that the mother probably had a big part to play in this case as well.
However, in this case if the son really cannot tahan living with the mother anymore, and money is not a real issue here, he should either have moved and left the flat to the mother, bought her a 3 room flat of her own, or moved her to a home. There are always other options, just leaving her bags on the door step is pretty heartless, even if she is the biggest b&*ch around, she still is his mother and has taken care of all his needs all these years