I am hurting my wife but I don't know how to stop

In the early stages of exploring polyamory, my wife initially desired the freedom to pursue connections while on business trips. While she had a couple of more serious relationships, they fizzled due to time constraints. My relationship with my girlfriend thrived, perhaps because of the ample time we could spend together during regular working hours, given my role as a stay-at-home dad and her ability to work remotely.

As for whether my wife intentionally avoided relationships, I'm uncertain. Regarding my preference for a monogamous relationship, I'm unsure as well. My dating experience has been limited to a particular type of woman, diverging from the values I was raised with after rebelling against my religious upbringing around puberty, I never dated women with the values I was raised with until my current girlfriend.

When we embraced polyamory, it seemed natural to be attracted to multiple people. But now I question whether this is my inherent orientation or a response to dissatisfaction with the type of women I pursued in the past.

While I fully accept my wife for who she is and her desires, I find myself no longer attracted to her. It's as if my preferences have shifted. It's not solely about casual sex; for instance, her choice not to shave her armpits, though empowering for her, doesn't align with my evolving attraction toward more traditionally feminine traits.

I observe this change within myself, particularly in public settings where I find myself drawn to different types of individuals. This is a journey of self-discovery, prompting me to reevaluate whether I still desire multiple partners now that I've identified my evolving preferences and found someone remarkable who could potentially fulfill all my needs.
It sounds like your needs and desires have changed. Many people go through periods like this. We grow, sometimes in a different direction from our partner. It seems you are aware of this and are looking to move forward to a different life with different values. There's nothing wrong with that.
Nothing wrong, except it's complicated. Because you love old life too. Because children. Because the old life won't let you snap your fingers and change everything to your liking. New life means co-parenting, which may not allow you move away from the city to a homestead, because children need both parents. And school. Or, losing kids to wife, keeping minimal contact, wife losing kids, keeping minimal contact, with an ugly divorce fight to start with.

That's it, right? You can't really pursue a different set of values independently of your wife while children are in the picture... For the next 15 years.

(I wonder, just my curiosity - did you grow up mormon?)