To DanceQueen: you may well be right. Overthinkingly, what strikes me is (a) the timing and (b) the move itself, which I've never seen her do in 22 years. Let me just say as a personal aside, DQ, you seem like an awfully cool Lady & I'm glad you check in on my thread from time-to-time.
That's my point, if we've been married for longer periods of time, we tend to know our partner's mannerisms, I don't think you would have mentioned these moves to arch her back and show off her breasts to get your attention if it wasn't out of the blue and something that wasn't common.
My gut instinct is that it's a gesture to get your attention. She also mentioned sex a few times, when people are separating and one spouse is leaving another, it just doesn't seem like a regular topic of discussion - out of the blue you start talking about sex and what she would have liked instead. Those to me are all signals that she wants to give you a bit of a "workout". Prove me wrong, no worries.
I read another comment, something to the effect of "I don't understand why she's doing this to you, seems like you're a great guy...", when women have affairs, it's not necessarily all about the husband, although they will use a poor marriage as part of the excuse to have an affair and have sex with another man. How does that saying go, "... resentment breeds entitlement".
