Tread, you and me seem to be in somewhat similar sitches. WW had/having what is likely an EA, POSSIBLY ending it or having already ended it, W keeps tossing crumbs but not acting like she is ready/willing to move forward with any work on MR and commit completely and fully to giving up the extra-marital relationship. No obvious path to separation and some overlay from the kids with whom you'd like to keep having family time.
Of course, looking at it clinically, separation of some sort, for your peace of mind and to get off the merry go round, but also so WW will know she could actually lose something here, seems like a good idea, but how to get there? I am in a similar sort of stuck place as well. FWIW in my sitch the past couple of days I have simply pulled back. I lay claim to the guest BR (weird-sounding, I know, and not the MBR, but it has the much better bed/mattress that both W and I prefer, and it is not a mess/wreck at the moment) and have stopped being as responsive to her. The family time angle is difficult because S18 is getting ready to go off to college in two weeks and is already stressing about it alot, so trying to avoid laying a big scene on him at the moment, BUT... I am going to start tactically withdrawing from such "events" starting tonight when W wants me to "go shopping with them". I plan to have other plans. Perhaps a little disappointment to kid here and there, BUT... think how disappointed your kid will be if you and your W split. Maybe better to endure a little disappointment now, in hopes that there is a bigger relationship payoff down the road. Not to mention which, if you do end up splitting, your son is going to have to start getting used to the idea of doing stuff with his parents separately, and your W should start to have to come to grips with implications of your split on your child.
H53/W51, R-ing 4/'18
"Do not arouse or awaken love until it so desires"-Sg.of Sg 2:7
"So oftentimes it happens,that we live our lives in chains, & we never even know we have the key"-Eagles III 1:3