Yeah.. I guess what I've been struggling with is if I want to be with the person after she's done.
You have no control over who she becomes. You can only cross that bridge if/when you come to it. I'll bet that if that time ever comes, you'll know your answer then.
It must be really hard to watch your W screw up her relationship with your Ds. She is driving that train, and there isn't much you can do about it. It's a shame really, but she's the one that will pay the price eventually.