Um, maybe you could just answer his question honestly and directly with whatever your reasons are?
Maybe: SO, we are no longer in an exclusive committed romantic partnership. It is not healthy for me to continue acting as though I am your sexual or romantic partner. It is not healthy for me to depend on you for emotional support through this. So, for my own sake I am limiting my interaction with you so that I learn how to live as a friend and co-parent with you, but not as a lover or partner. My decisions are based on your choice to leave our R. This does not mean that I will absolutely be unwilling to work on an R with you or reconcile, but it does mean that I will not stay in our old R by myself. I care very much about you and your happiness, and right now this is the best way for me to give you what you want while respecting myself and my own needs.
Best,
Oldtimer
P.S. Sure, go dark, GAL, whatever. What you need to do is detach... Consider how you put off responding to in-laws' emails for some time. Or how you sometimes might not immediately respond to a message from an old friend or sibling... Not because you are mad at them or even avoiding them, but rather because it is NOT the case that your scrutinize/obsess over every tiny facet of your interaction with friend/sibling and think your own happiness hangs in the balance. Be a friend. Friends talk more or less at different times for various reasons. But, you don't act/react as though your own emotional well-being hangs in the balance. Nor do you expect their happiness and world view/goals/plans/etc... to hinge on whether or not you give them the wrong look, use the wrong word, take the wrong tone, dress the wrong way, immediately text them or wait 5 minutes, etc... It would be CRAZY to think you have that much power over your friend. And, you don't have that much power over SO. Detach and own your own emotions and reactions. Let him have his, he will anyway.
P.P.S. You communicated the basic facts to family. Do nothing else. IN NO WAY try to control their interaction or manage their R with your SO. It is not your place, stay out of it.
P.P.P.S. It seems you may be feeling better with taking charge of how much interaction YOU want and respecting yourself in all this. I'd stick with that for awhile and see how it goes. Trust me, he is not going to forget you. If anything, he will appreciate you more and begin to be more objective about things with less repeat old stuff to be reactive about.
