It's a tricky one. Stick to your guns is easier said than done. I'm a living example of not being strong enough to apply tough love or stick to my guns.
You've made the right decision. Don't leave the MBR. I am back in it after being out of it, and now WW is moving out. (Sleep reasons, not EA, according to her).
Many of the things in your sitch echo mine. The only thing I cling onto is that the OM is in another country so there has been no PA yet. I am sure there will be at some point.
What are you thinking about the bed situation? Are you going to help her assemble it? Move things around for her. After finishing moving a mattress on Saturday that WW had already started moving, yesterday I decided to tell her I wasn't helping move the bed frame (she wanted me & SS to do it) as I wasn't having anything to do with her EA. That blew up into a most horrendous argument. Does your sitch follow this pattern, and if so, how do you deal with it?
How are your GAL activities going at the minute? Do you struggle with working long days? I'm similar in that I am out of the house close to 14 hours a day, and then want to see D when I get home. I imagine you are the same with your S. DO you find time on weekends? Does WW try and make you feel guilty?
Anyway, stay strong - I'll keep reading your sitch and cheering you on brother, you can do this.
-- Me: 47 WW: 35 SS: 17 D: 5 T: 7 yrs Engaged: 2 yrs OEA confirmed: August 17 2016 ongoing since April 2016. OEA continues (with occasional breaks) BD2 - W says will visit OM in Jan 18