mybest, I went back through and read most of your thread. When I reread your original post I got that sinking, he is cheating on her feeling.
Let me put it to you the way another marriage/divorce avoiding expert (not MWD) put it: he doesn't need his own place to fall back in love with you, he needs his own place to sleep with other people.
Sorry to put it bluntly, but most guys don't wake up one morning and go "I am not in love with my wife anymore so I am going to move out." I wasn't in love with my wife for years, and never did the thought of leaving or separating enter my head. If I had met someone that might have changed.
But as others have said, this doesn't really change your approach at all. Unless infidelity is a deal breaker for you. Have you asked him point blank if there is someone else? (I would only do that if infidelity is a deal breaker for you.)
Also, if in the 6 months he is separated, if he sleeps with someone else would you consider that infidelity? Does he know how you feel about that?
M(53), W(54),D(19) M-23, T-25 Bomb Drop - Dec.23, 2017 Ring and Piecing since March 2018