Your situation bears many similarities to mine. My exW had a string of EA's and I eventually caught her in the last one. After that I got the ILYBINILWY, BD, set on divorce, etc. etc. I was able to DB and we reconciled and had another three years together at which point, like you, I suspected something was up, caught her at it again with a new coworker and got divorced.
You and others have come here lately referring to "The 180" and talking about it as if it means walking away from their spouse and giving them space. From my read of MWD's books, "180" refers to evaluating your spouse's complaints about you, deciding which you want to remedy and then addressing them -- i.e. if you used to be sloppy be neat. Not super important but I'm not sure where this new interpretation is coming from because people now seem to think it means "don't pursue".
Regarding your situations, no radar is as fine-tuned as that of a cheated-on spouse, so I would say if your radar is telling you something is up, it probably is.
Does it matter though in the context that she wants to separate and/or wants out? If another person is involved or not, the facts of your relationship are the same.
I think the prescription is the same no matter what: don't pursue her, address your own issues (180), get a life, and act as if you're fine.
In the case of my exW, her needs were not being met in our marriage -- it was a classic "Five Love Languages" challenge where we were sending and receiving on different channels and weren't aware of it. Unfortunately, she chose not to voice any complaints or articulate any desires, perhaps in the interest of avoiding conflict. As a result, her resentments built to the point that she sought an EA and felt justified in doing so. I think at that point she was pretty checked out.
When we then reconciled, I think it was the path of least resistance, or something she felt she was doing for the benefit of the kids and the family and her EA had ended. I don't believe she was committed to the M at that point, so really it was just a stay of execution versus a real reconciliation.
I consider that to be a blessing for me, because I got three good years to be the best H I could be, to "bring it", and to leave the marriage with no regrets about my behavior or my contribution to it, I was able to leave with a great degree of peace. Hopefully you've had the same experience since your W's last EA.
If she's walked several times before and wants to walk again, chances are these are her issues that she doesn't want to address that you may or may not be exacerbating, and she doesn't believe in her heart that she can navigate back to "happy" with you.
As you probably know, the only way she's going to overcome that deeply held belief is for you to open the cage door and completely cut her free. If you engage in a relationship with her again it should only be under the conditions that:
1) She sees you as someone of extremely high value 2) She views a relationship with you as something much better than a life with someone else or a life alone 3) She's willing to work to win you
Without those three things, she's going to walk again down the line, because she really doesn't have the motivation to work with you to change anything, your relationship will keep seeking the same equilibrium it has had because of how your personalities and issues come together.
Given that you have to make things worse before they can possibly get better, separation may not be a bad choice, but I would advise pursuing a separation with the same rules you would have if you were divorced, which is to say that you don't continue to comingle your lives (aside from the kids) and you are free to live your own lives without social accountability to the other person.
That way she can really see if that way of life is better or worse for her. Prepare yourself that in the beginning she will view it as better, mainly because she'll find new found freedom and has convinced herself that its what she wants. It may take six months or two years for reality to set in, but it certainly will.
My advice would be to lean in to what she wants, agree to separate, and work productively with her on the plan with the presentation that you're on board and plan to enjoy this change also. That's going to make her wonder. You want her to wonder what you're thinking, and from this point forward you shouldn't tell her anything about your frame of mind -- nothing at all.
Acc
Married 18, Together 20, Now Divorced M: 48, W: 50, D: 18, S: 16, D: 12 Bomb Dropped (EA, D): 7/13/11 Start Reconcile: 8/15/11 Bomb Dropped (EA, D): 5/1/2014 (Divorced) In a New Relationship: 3/2015