Honestly, sometimes don't you just want to yell "for pete's sake, who's the adult here?"

I've seen parents who don't confront their children because their "relationship" is more important to them than actually parenting well, which is what your DH and his ex sound like...

Just keep on doing what you are doing, and good luck. Hope the holidays go well...

And just as a thought -- sometimes no matter how well you parent or step-parent, there are things beyond your control, especially with a young adult/late adolescent.

Sock