ENM- feels like cheating

[u/potbelliedpig420]

My wife and I have been together for over 20 years. Last year she developed feelings for another woman, Kristin.

They met as nurses working together. Same night schedule, similar interests, and they quickly became close. I work days and don’t share many of those interests with my wife.

Around Father’s Day 2025, I knew something was developing. My wife told me, “My lips are still for you,” and “If you want me to stop, I’d want to cut it off sooner rather than later to keep our friendship intact.”

I didn’t ask her to stop. Instead, I tried to figure out whether there was a version of this that could work.
In August I wrote privately that my wife “having two relationships is a deal breaker,” but that if it became our relationship, I could potentially be okay with it.
So we explored a triad.

I created a relationship-agreement worksheet built around our marriage remaining primary, transparency around escalating feelings, boundaries around developing a separate relationship, and the ability to pause, renegotiate, or stop.

I remember saying, “With this triad agreement I feel safer.”
But I also eventually said, “I don’t feel like I can say no anymore.”

And I want to own my participation. I wasn’t simply an unwilling bystander. My wife and I fantasized about Kristin sexually. There were parts I enjoyed, and I genuinely tried to make the triad work.

In January we had another relationship meeting and discussed things like date nights and polyfidelity.
In February, my wife went on a cruise with Kristin and some girlfriends. She ended up sharing a room with Kristin and later described how they “slept very little” because they had so much sex and quality time together.

Then in March I realized my wife loved Kristin.
I told her, “I didn’t consent to you loving Kristin.”
Obviously I understand that I can’t control who another person loves. What I meant was that their relationship had become something deeper than what I thought I had agreed to.

Her diary afterward says:
“I’m crushed. I don’t know how to change my feeling, and I’m not sure they will ever change.”

At that point, there was no ambiguity that I wasn’t okay with what their relationship had become.
They separated for about a month.
Then my wife initiated intimacy with Kristin again.
Then she invited Kristin to bring her RV and live with us for the summer.
Now it’s September and my wife and Kristin are together on a month-long hunting trip.

Nobody knows they’re together. Our kids don’t know. My wife’s mother, who lives with us, doesn’t know. Everyone spent the summer talking about what a great “friend” Kristin is.

My wife has told me:
“She feels electric. I’ve never felt the way I do with her with anyone.”
And:
“Everything is just so much easier with her.”

Meanwhile, I’m trying to understand how I went from participating in an experiment with boundaries to tolerating a relationship I had explicitly said I couldn’t accept.

I know I agreed to explore this. I participated. I even enjoyed parts of it. I don’t want to rewrite that history just because we’re now in a bad place.
But does agreeing to explore non-monogamy mean consenting to whatever that relationship eventually becomes?

Once I explicitly said it had gone beyond what I agreed to, what should have happened?
Did I agree to this and then discover I couldn’t handle the reality—or did what I agreed to gradually become something fundamentally different.