There is a great book by Melodie Beatty called 'Co-Dependant No More' & 'Beyond Co-Dependancy' ... I think last time I saw it, she combined the books.
I hope that you do see what Pom is saying about not getting tangled in another couples issues.
It has a way of turning on the wrong people ~ especially as difficulties mount.
Avoid the projections and misunderstandings by remaining their friend, but releasing their issues.
Listen, love them, and hope for the best.
Peace and Support,
Night
xoxo