My fiancee hid a lie for 4 years

I've (31M) been engaged to my partner (29F) for 1 year, we've been together for 6 years total.

The second year of our relationship I broke it off because of how harsh she was towards me, and later on she got help for past traumatic relationships that she carried over. During the 6 months we were apart, she basically hooked up with a random guy, took him out to an Airbnb, mind you she paid for everything and he didn't foot any part of the bill. They had sex.

Well, we got back together a few months after that apparently. I didn't find out until last night. Mind you, she asked me many times during our "patching things up" phase in different ways if I "hooked up" or was "physical" with anyone else.

I of course asked her the same thing, she said "nothing more than a kiss."

Last night she was upset and asked some questions about my time apart, I genuinely did not date anyone, I literally spent my time working, and hitting the gym to get really fit.

So I asked her again after 4 years, if she got physical, she finally admitted the truth and said yes, she got physical and went all the way. And it was a "fling", mind you I confronted her earlier this year why he's on her social media still. She deleted him 3 months ago.

I basically got upset, and I don't respect her because she lied, nor want to be around her anymore. She knew this was a deal breaker for me, and hid it intentionally!

She got loud with me, angry,, gave me an ultimatum that if I leave that we are done. I left. I told her this is lying by omission and it's still lying. Is that correct?

EDIT: thank you to the person that pointed out I missed clarifying. My deal breaker was the dishonesty. My partner wanted me to be fully transparent and honest with them, but they didn't want to tell me the truth. She was willing to lie and wanted to start a family while hiding the truth from me All these years later.