I would also recommend Hold on to Your N.U.T.s by Wayne Levin.
One of the biggest things about the "Nice Guy" problem is we tend to shoulder problems without complaint, but instead withdraw. Setting up boundaries and defending them - with ourselves as well as with others - is a necessary tool.
Don't be so hard on your self. We all fuck up. We can only grow when we admit our faults, deal with them, and move on.
As men we sometimes do things that we often regret. We have to live with those things till then end of our days. Some of those things we do, like stray (what ever the reasons) are best kept from the people we love and only shared in the company of other men. I'm not saying what you did was right, but I'm proud of you for seeking out help and console to make your relationships strong and prosperous. Have you thought about joining a mens group? That might help a lot. Check out this book, it helped me when I was stuck.
This sucks. It is an old story. And It Sucks. Someone has to change the dynamic. One of you. And it likely has to be you, since here you are seeking advice.
I am concerned about "hope she doesn't take it the wrong way". And I am reading between the lines here, so if I have it wrong here, please accept my apology. Are you a milquetoast? A yes, dear? A Nice Guy? When you say you have taken on ALL the labor, I wonder. Because how can that be? You work. AND clean. AND cook. AND manage the kids. And she goes to college. That is highly imbalanced.
Here is the sad truth. And it sucks. But despite what we think we hear in popular culture and whatnot, it is really hard to maintain respect and attraction for a milquetoast. (Sorry, I hope I am not coming off as mean. Not intended. I am 52, and I would bend over backward to be married to a guy like you.) People don't do it on purpose. But eventually you wind up taking someone who can't stick up for themselves for granted.
There is a book. STRONG DISCLAIMER I have not read it myself. But as a person who has interest in relationship and marriage topics over the years, it has come up as really helpful for men who are in this situation.
https://www.amazon.com/Hold-Your-NUTs-Relationship-Manual/dp/0979054400
N.U.T.s refers to " Non-negotiable, Unalterable Terms" and you will see in the description it is about limit setting and getting what you want within the framework of your own character. From what I have heard, it is not how to become a mean old misogynistic asshole but how to become your best self when your kindness and giving nature is running the risk as being expressed as door mattishness. And, in the process, it can help rekindle the respect, affection and admiration that she may miss without even knowing it!
Good luck to you!!