Everyone! Thanks for the encouragement and valuable advice.
Maybell, I looked at your signature and noticed that the timing of events in our lives is similar, i.e. our ages, kids ages, length of M, even the date of D-day are similar, yet you seem to be much more together and empowered. Kudos to you. That was just an observation from which perhaps I can draw strength.
As far as complaints pre-A, she did not have many. Intimacy was good and pretty regular, I would tell her how attractive she is, she had time to start her own business, we tried to do date-night weekly, I still bought her flowers on occasion, we did not fight/argue seriously, I never told her how to spend our money, I adored her and championed her to everyone. Occasionally, she would complain that I am not home enough in the evenings and that she could never go out or have time to herself. I would always counter that she could go out any time, but she had difficulty leaving our youngest S. I used to joke that she had separation anxiety.
After D-day she said, in retrospect, that she did not have her own voice, that she adopted all of my convictions (vis a vis religion, parenting, values, etc…), that I was too controlling, and that I was not "there" enough for her. Initially I signed on to the theories she concocted, blamed myself, and even apologized for it. In response, I relinquished all control - giving her free reign, came home an hour earlier daily, gave up some commitments (e.g. bible study) and forgave her. She responded with disdain and by asking that we separate. A few weeks later I caught her with OP for the second time. I think she needed to find fault with me in order to justify her actions. Obviously there was a flaw in the relationship and, in retrospect, I would tend to get my way more often than she, but I really did not perceive any red flags nor did she raise any until after the A was disclosed.