Oh upgrade.....I feel so bad for you. My only advice regarding confrontation about OM is that when I confronted my H about OW the day after Valentine's Day...it kind of blew up in my face. I asked the question "do you still want to be married to me" his first response was yes, but then over the course of a few hours and us talking, he convinced himself that our issues were unresolvable. I wish I had never confronted him with the valentine's day card with "her" initial on the envelope. I wish I never found the notepad that had the name/location of the place they went on V-Day. I wish I could take it all back....even if things were strained before, the "move-out" talk would not have happened. EA/PA is unconfirmed but highly suspected. My H is still living here, but similar to your W makes himself very scarce. Gym twice a day, long bike rides on weekends, etc....
So if I had a do-over, I would wait to confront. That's just me but I do wish YOU the best with whatever you decide.
Your post really touched home and I feel so bad for you. Keep your chin up!