He was in Belgium for five minutes and returned to complain of shell-shock, comparisons with the guys on the Somme were odious.
Shell-shock (or PTSD) isn't quantative! It's not a case of the worse the experience the worse the shell-shock
Some people go through terrible ordeals and don't get it at all
Given the type of man he was, he would probably have agreed with the WWI view that shell-shock was a sign of 'weakness', and not admitted, even to himself, that he had a problem. There would have been very little support available even if he had been willing to look for help.
There is also the fact that he had spent most of his life giving orders and expecting them to be obeyed
Unfortunately there are still cases of soldiers (suffering from PTSD or not) being unable to fit back into civilian life
None of this excuses his behaviour towards Patrick's mother, but it might help to explain it
Linda