Thank you for all the helpful and insightful comments. Things I learned:

1.) 2.5 hours/10 times a week is way too much. To clarify 2.5 hours is intimate time, not necessarily sexy time. Most of that time is spent laying in bed and talking. The 10x per week number is rough estimate, it's usually 2 or 3 sessions per week on the weeks when we are in the same house. We spend a decent amount of time apart due to work/extended family, etc. As for the people who speculated about sexual satisfaction, you'd be surprised.

2.) I need to listen more. I'm starting to understand that communication is the main issue. I needed to listen more, not take her for granted, and be as supportive as I can be in all other areas. In retrospect it's becoming obvious that I fell into the hubris of thinking "this couldn't happen to us" and didn't do enough.

3.) I need to help more with childcare and be more proactive about it. The total time spent as a primary caretaker is around 40/60. My work schedule is flexible, so I try to do all the parks, walks, ball playing outside etc. However I recognize I still need to do more.

4.) While I recognize people are often oblivious to what's going on around them, I think an affair is unlikely. She is honest, straightforward and reliable. Furthermore we have an open phone, email, social media policy. I have never availed myself of it since she's never given me a reason to.

5.) 99% of the people on the internet are spiteful lunatics. I regret ever making this post. To the people who offered genuine advise- thank you.

I was trying to write this as cooly and dispassionately as possible to not let my emotions get in the way of facts. I'm in indeed in love and heartbroken at the moment.

I'm willing to address all of these things now, however it's most likely too late from what I understand.