Jase, Our situations are pretty similar. I feel for you...man this is tough.
My W had an EA with a coworker. It was slightly physical, but no sex (couple make out sessions). I know this from snooping early on, I wouldn’t have believed no sex if she had just told me that. It ended and he is now married, but they still work together. It was about a year ago that it ended. I think the willingness to throw away the family for something shallow like that has to do with where their head is at, not as much about the validity of the relationship with OP. They want what they want and feel they deserve it. If they are giving so much mind space to someone else (regardless of if reciprocated or acted on), they leave no mind space for us. Hard to work on “us” if daydreaming about someone else (real or imagined).
I also have trouble with boundaries. I have been with her for 20 years and have trusted her unconditionally. We’ve never had the need for boundaries because neither of us have crossed each other like this before. I don’t recognize what boundaries need to be set until she crosses one. I imagine that is a common theme.
Just keep working on you and the kids. Vent to us and ask questions all you need and we’ll be here for you as much as possible. Just try not to initiate R talks. That has been my biggest fail. I’m a talker and a fixer. I have never liked to let issues sit. It is important though. For now, you guys are roommates. Pack your relationship in to a box and put it on the top shelf for later. It will be there if you need it, but for now it shouldn’t be your focus.
Sorry you are here, but you are among friends who truly understand what you are going through.