Why are you moving out? Seems that since you are the primary caregiver you should stay in the family home.
I would stop reiterating that D is not what you want. You stated it once and that's enough. Her threats are probably to make sure you're on the hook as plan b.
I have a hunch that the ea is still going on and she knows it's wrong but can't end it due to the addictive nature of an affair. If not she's probably looking for that high again.
