The change to you was sudden, but likely she had been unhappy for quite a while and you just didn't know it.
Actually, I knew it. I was also sick of the MR. The sudden change I am talking about is the drastic going from regular affection to going incommunicado in one day. As she said herself during BD, "D was unthinkable 2 months ago", but apparently it was like "a door opened when she got away from me for a while" (she meant the travel).
Haha I am aware that her revised MR will be the first topic and first bonding with the OM. And the OM will probably be like he has just won the lottery as W is quite a hottie even at ML . Over the years I have trusted her completely even though she is validated day in and out by potential suitors and young horndogs, as I was confident of her family values as well as about me. We would frequently joke about people hitting on her all the time. So, the A came as a massive surprise. If I were to imagine she would D in the future, then I would also think it would be clean rather than becoming a WW. And I know that the promise of a rosy future with her AP is the top reason for not recommitting.