Wether in a quad, or any other relationship style,....sometimes we have to take the 'hard road' . We have to pull back, pull away, and make sure issues are dealt with, instead of forging on.
It`s one of those things, that is easy for us all to recognize, but in the moment, it can be hard to follow through. It seems most people prefer to carry on, until a explosion happens, wishing for the best.
If you are able to put the brakes on, and pull-away for a bit,..you might be able to help them as 'friends' first. Help them under the relationship you`ve had for many years. The relationship with the most experience.
They might get mad. They might be upset with the 'brakes' being added. They might go further down the rabbit hole, before they hit rock bottom.
There are many things that can happen. Just be true to the friendship, dont desert them, but dont pretend like their marriage problems are no big deal. Be honest, and upfront, without being overbearing.
Yes, relationships are either broke, or made stronger this way, but whichever happens, at least it`s true.