Am I missing something?

I am the ideal father and family man. If I am not working providing for my family, I am spending time with them. Problem I am facing is my wife of 20 years recently had an EA with a coworker. Her reason is that we started to drift apart mainly due to my obligations with my teenage daughters, which is where all my free time was devoted to. Is is not that I ignored her, still told her I loved her, complimented her, flowers on occasion for no special reason, cards etc. Our intamacy has been strained mainly do to my exhaustion at the end of long days. I understand I may have hurt my wife by not providing as a husband over the past couple years due to my many commitments with them. However, I do not understand her way of thinking and why she chose to have an A. She told me that we were drifting apart but I chose not to believe her and said we will soon have more time to spend together as our daughters soon will not need us as much.
My life is my wife and family and am having a very difficult time with this whirlwind I am living in.
Can anyone comment or past experiences? Have I been a bad husband to deserve this? I just don't understand it all!!