It's a toughie.
Reaching out ?? Or stirring the pot ?
For me it would be; their relationship is their business to work out. It's easy to get dragged into drama, but it ain't my problem to fix. They are adults. So it's not something I would bring out into the open. But I don't have to pretend that I don't know. If someone wants to discuss it with me, I can listen, even express my feelings about it, but don't tell them what to do. I don't have to take sides.
I hope that I would deal with my own grief and anger about it in a way that helps myself, without feeding into the drama; talking with a partner, a counsellor. I would also be able to choose how involved I want to be with a person , so that I look after myself.