Sorry, I am in the middle of a big project and can't really follow another thread.
A couple of quick things --
-- leave MIL out of it totally. Wait until things are resolved one way or another with H to work on that R
--"I do not feel prepared to get a divorce right this second; he doesn't want to give up the "option" of dating. When I tried to enforce the idea of no dating he immediately said that we should skip separating and get a divorce if that is how I feel."
He has told you he is not going to respect a boundary that you want if you merely separate. Divorce does seem a logical consequence.
By all means, completely let go. It is the best chance you have. Whether you do that in the context of a sep or a D is really up to you. Some people don't manage it even after D. But, you aren't really holding onto anything. H is already gone. Your not letting go simply builds a big spider web around you that H must avoid if he is to retain his autonomy. No spider web = H can come closer if he wants to without giving up part of himself.
