Family Dilemma taking sides

My fiance's aunt (64) is thinking about divorcing her husband (77) This issue started after her husband had a falling out with the niece. They have no children and are loaded so the aunt from time to time gives lavish gifts and cash money (more so to her niece than others) -without her husband knowing. She's now breaking her silence that she gets emotional and mental abuse from her Narcissistic/egocentric husband. I don't know the side of the man that way but I could picture it happen. However, I do have a good relationship with the couple.

We had coffee the other day and she was saying he was practically stalking her and wondering how she spends her money. Afterwards, I then said I feel bad for him too because he's dealing with a lot too. Old age, he's estranged from his family, he has no children, his long time friends are passing. Her response was, "if you knew the way he talks to me and belittles. He's been like this ever since I know him"

It felt like I had to take sides now and have no empathy. To his defense, she left her husband for him, over 40 years of marriage and knowing how he is and letting him treat her the way she says he does all through the years. I'm just not sure I can put all the fault on him. Besides, it's their business. But it sort of feels like I'm getting pulled to take sides and I'm not sure how to approach this matter without being insensitive.