Hi
@22kate - I don't have any direct answer as such but I do empathise with your situation as the same thing happened with my husband and our son.
There was no obvious trigger for it that I could see. My husband was the kindest, most gentle of men and my son's character was exactly the same. My husband was diagnosed at a young age (58) and our son was still a teenager, living at home while attending university.
I've often wondered if there was some underlying jealousy that had come to the fore. People always praised our son for his kindness and academic achievements and I know that my husband would have liked to have gone to university himself - he was certainly clever enough but obstacles were placed in his way.
Anyway, for a time my husband developed a very nasty opinion of our son and said many detrimental things about him to me, though fortunately not directly to our son. Having said that, our son knew something was up by the way he would often catch his father glaring at him. Fortunately my son also knew how to read the signs and would often go to his room, hoping it would be a case of 'out of sight, out of mind'.
When I didn't back up my husband's opinion (I simply diverted the topic) he saw that as me being in league with my son. I could see that things were escalating beyond my control and spent two weeks trying to get help from the home intervention team but nothing was forthcoming. It took a crisis to happen (my husband attacked our son out of the blue) and then my husband ended up temporarily in a mental health unit.
It was an awful place but it was also the best thing to happen because they got my husband on the right medication and, after a couple of months, he returned home without all the paranoia. I am pleased to say my son and husband returned to their previously great father/son relationship and remained extremely close until the end.
So, however dire things might seem at the moment
@22kate please know that medication can help and situations can change for the better. Even now, almost three years since my husband died, and despite all the huge stresses along the way, my son says his father's dementia ended up bringing them closer to each other rather than tearing them apart.
As a mother and wife witnessing this scenario play out between two of the people so close to me I understand your anxiety - but I can also say that it brought me great comfort in the end when I saw their relationship completely restored and strengthened.