Finally heard back from M, and yep...she's out. What was a nice moment for me was actually uncomfortable for her. While she doesn't judge what my wife and I are doing, she says she has a much more conventional view on marriage, and doesn't care to spend time connecting with someone who is going to stay married. But she still wants to hang out in the same manner that we always have, so great.
I was afraid our last outing had screwed that up, and I'm very happy to know that it didn't. We might go out next week...not sure.
But romantically...back to square one. Oh well.