Wow, S sure is perceptive. Don't the spouses know this hurts their kids?
At least my H had the sense to totally keep the R with OW out of the home. The one and only time she called him at home was the time I "caught" him in his lie.
I feel that your H is done with OW, because you are going to succeed, and it can't happen with her around. You are working so hard.
Definitely, stop being so predictable. Don't you think that's what H saw in OW? Challenge, chance of being caught, someone not predictable. I think in your sitch it is the case because he was so stupidly open with it that you and S knew about it. So, be that OW, challenging, new, exciting. You can do it.