My aunts and uncles are very nice, all of them, and they are all still married except for one of my father's sisters who has divorced her husband.
They have kept the reasons for the divorce to themselves (and presumably their kids, my cousins), so as far as I am concerned, he is still my uncle, and I can only go on how he treated me when I was younger, which was very generously.
If it transpired that he had been abusing my aunt, then that would be different.
I don't have any brothers or sisters, so the only nephews and nieces I'm likely to have are the two toddler sons of DW's younger sister. Since we aren't able to have children of our own, I'm determined to be a good uncle for them - indeed, the only one they are going to have.
I think it's especially important in my case, as occasionally the morbid thought occurs to me that if anything happened to my sister-in-law and brother-in-law, DW and I would automatically take over their upbringing.