AITAH for lying to my wife that I'd forgive her cheating?

When me and my wife first started dating, we had a talk about cheating.

I straight up lied, and said:

"If this ever happens, I need to know straight away, if you tell me, and it only happens once, I think I could forgive you"

Fast forward 5 years later and we are married.

A couple nights ago, she came up to me and asked if I remember our talk, I said which one (we had a lot of talks like that).

The then reminded me of the cheating talk, and confessed she slept with a co worker at a recent company party.

I was mortified. I packed my stuff and left, she begged me to stay. I couldn't, I needed to cool down.

We talked yesterday, and she again reminded of our talk early on, I laughed, and said that I never intended to forgive her, and I only said that at the time to make sure she confessed if it ever happened.

I'm still planning on divorcing her, nothing can change my mind about that, but my wife said what I did was manipulation.

Was I the asshole for lying about forgiving her?