If you're partner lied to you about something while you were on break would you dump them?

So me in my girlfriend have promises to be honest with each other about everything in our life. My girlfriend and I took a short break 3 months ago she ended up really wanting me back. So we got back together after along talk she randomly promised me she has never slept with anyone else but me her whole life.

I ended up finding out today she lied to my face and that the guy she seen for 1 month she slept with. I don't 100% really care since I do feel like since I'm the only guy she been with that she needs to experiences other guys etc. Agin I don't really care that she slept with the guy but we had a conversation about him and she lied to my face. My girlfriend knowns being honest is something thats really important to me and that if I find oneie then I just won't truest you anymore and will doubt almost anything you say. In the past year of my life I haven't told one life not even white lies since life has changed me. I'm always honest about my feeling but try voicing how I feel in a caring none hurtful way.
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Update I check the text I've seen and she may have seen him this month while we were dating. She told me they were friends but her whole friend group cut him off after he cursed evilness out. The text messages says she will not be taking him back but from what I seen she may lied to me and have been dating him this whole time after telling me she wasn't and were just friends now since he's in her friend group. Will talk to her tm about it if true anything between us even friendship may be gone
If you're partner lied to you about something while you were on break would you dump them?
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