Betsey, I have also made a small change in my sitch too... I do think MW needs to miss you all and needs to reap the benefits of what he has sown... let him miss you all. Let him feel what it is like to not be an "insider" at your home. I definitely agree with him calling, and I would ask for his key. He should not be able to act like he lives there.
Don't know about the legal separation thing... you will have to decide on this. I might make the change of boundaries first, then follow up with the legal separation after you monitor results. Kind of a one-two punch.
Relax. Appreciate. Be calm. Laugh. Enjoy. Be secure. Be loving. Be loved. Don't personalize. Don't ASSume. Accept. Be grateful.