Re: Going through R but back to old habits.
It sounds like you don't want a relationship, you want sex on demand. Unless you're happy with random hook-ups, that formula typically doesn't exist, and certainly not in a long-term relationship.
If a marriage is "awesome" as you put it, it's because both partners are invested in each other, make spending time together a priority, and continually engage in activities to foster an emotional and physical connection.
Are you attempting to initiate sex and she is denying you? Or are you assuming she doesn't want to have sex? What energy are you offering to elevate sex beyond "routine"? Have you had an open conversation with her regarding the state of your relationship, or do you just disappear after your parenting duties for the day are done and then wonder why your partnership is suffering?
She is a person, just like you, with independent wants, needs, and hopes - not just a parent or housekeeper or employee. When was the last time you both chose to engage with each other as people?
No marriage is "awesome" by chance. It takes effort and focus to ensure your romantic relationship is a priority, and you both are selfless enough to focus on your spouse, recognizing and trusting that your partner will be there to fulfill you in return.
You can both change your path, if you choose to. She doesn't have to choose an affair, and you don't have to choose to marginalize her when it's convenient for you. If you're not going to pursue a better relationship with each other, then divorce.
My spouse is MrMathias You reap what you sow, so think carefully about what you choose to plant.