How can I support my divorced son?

[Lois22]

My son and his partner have been separated for three years and neither is in a new relationship. They have a five year old daughter. They live a couple of hours away from us, but very near her family, with whom we maintain a friendly relationship. My son had to move out and now lives a short distance from the original home. The problem is that no matter how hard my son tries, no matter what lengths he goes to, he cannot seem to 'do enough'. He works full time, goes round morning and evening to take my grandchild to school and then give her dinner/put her to bed. They still do numerous activities as a family and with her wider family, which is obviously nice for my grandchild, but no matter how far my son tries to accommodate the situation, he is still made to feel 'guilty' in some undefined way, and is regularly subjected to tirades of verbal abuse, fits of uncontrollable crying and shouting, often about complete trivia unconnected to the child, which often come out of the blue. I have lost count of the number of social occasions which have been spoiled for our family and her own by a tantrum about some vague imagined slight or issue. She has a supportive family close by (which my son doesn't) but has up until recently led a life apparently sheltered from any harsh realities and entirely free from care. She does not seem to understand that in comparison to many young parents she has things very easy. Nothing is ever right. Last week they both worked very hard to put on a lovely party for my grandchild but at the end my son had to leave her crying and ranting as he had to go to work at 9pm and she had taken offence at some mild remark made by a guest. It ruined the whole day. My son is a kind and sensitive man and says he feels in a permanent state of guilt and anxiety awaiting the next tirade. He also obviously feels trapped due to wanting to spend as much time as possible with his child. I don't want to interfere and I haven't, but he has suffered from depression in the past and I worry that he is under terrible pressure. He has nobody to talk to about the situation and I only get occasional outbursts because he feels a sense of loyalty to her, however, it cannot be right that her emotions and lack of maturity set the entire agenda. Does anyone else have experience of this type of situation?