I third Eskie.

I actually told a very close friend of mine, as well as my niece, that whining about their SO's are off the table if we are to remain close because they have knowingly (one is a cheater and the other is a man child) chosen to stay with these men, so in my eyes, lose the right to complain about them.

At least to me.

This boundary has done wonders, as I have been able to retain my respect for them and my relationship with each of them is back on firm footing.