Maybe in future in instead of saying 'it's for the best' which could be read as 'this is what I want to' - you could say. Okay, I don't want our M to end, but if this is your choice I respect that. What I'm not willing to do is live in an open M, so if you want to continue seeing OW, I can see why you would want to move out.
And then I would go as dim as possible for a good while - enjoy being off the rollercoaster and make some nice plans for yourself.
I'm sorry things have come to this point - but I actually think the bouncing back and forth is the absolute worst scenario for any LBS, so to be out of that will be a positive I think.
Take care xx
T 13 M 7 Me 48 H 46 SS 15 BD 7.14 PA D final 5.16 (H filed)
We receive & we lose, and must try to achieve gratitude & embrace with whole hearts whatever of life that remains after the losses - Dubus