Its bad but at least they’re both still alive and you can still see them both.
You most probably dont know the full story of their marriage and the stresses that went with it and probably will never know as its their business and no others,not even their families.
They may have stayed together for many years past the true marriage breakdown even if they were both making each other unhappy out of various duties to family or other concerns,so let them have their happiness now.
If the seperation is an emotional glitch then they will soon find this out and always have the chance to reconcile but I would expect this to be very unlikely going by what you say.
Sometimes divorce is the best option for happiness,my own particular parents are both dead now but I grew up with a psycho headcase,sadistic,alcoholic father who would use extreme violence after drinking several times a week on us kids and our mum.
We got used to the sound of her screaming while we quivered in bed terrified that we were going to be next.
He would have undoubtedly killed her in the end eventually but luckily for us he died of T.B. when I was twelve.
Different from your own situation I know but we prayed for our mum to leave him but we always knew that he’d track her down if she did.
In case anyones wondering I’m not looking for sympathy here or feeling sorry for myself it was just part of life,many people lived through the Blitz,we survived our parents and I’ve never once felt compelled to mug old people as a result of my childhood.
So yes its a shock to you now but you WILL get used to it,try not to let your present hurt show too much to them as they themselves are going through a difficult time and they may feel pressured into returning to a situation that made them unhappy or their feelings will be made worse by having the guilt of upsetting you on top of the other stresses.
They’ve given up one hell of a lot of their lives nurturing you now its your turn to be brave and to reassure and support THEM emotionally.
Let them have THEIR chance at happiness after all this time.
And sixty years old in this day and age does not necessarily equate with being physically helpless and being mentally deficient.