Many people think an A would be a deal breaker... until they find out their spouse has an AP. Then... the BS (betrayed spouse) isn't so sure it's a deal breaker, after the initial shock wears off.
That said, I find it quite interesting that you didn't feel the M was that bad. Because your statement just before that was, you stopped wanting to do things with her. IOW, you didn't want to be with her, so you stopped doing things with her... and she noticed... What I mean is, how could you think there wasn't a problem in your M to a W you didn't want to do things with?
Do understand that I am sure you felt your W wasn't always pleasant to be around. I am pointing out what we remind people about DBing. Changing ourselves can change our sitch. In your case, at least that ONE change in yourself, changed the sitch which helped lead to the breakdown of the M.
Did her personality begin to rub YOU the wrong way? Has this always been an issue, but has been getting worse? What else led to you not wanting to do things with her?