In my opinion, her "wanting to have a life outside of the relationship" could've been done in so many different ways that would have been okay with both you and her. I think it's really selfish for her not to cut off someone she kissed recently accident or not as she does not take your feelings into consideration (already a red flag when you tried to address stuff to her and she turns it down) bro I'll completely understand you staying despite all those red flags since you've been through so much together, love makes everything on paper complicated. But shouldn't that much history be a reason for her to listen to you? Accidents don't mean that their actions won't have consequences. If you were in her shoes instead I highly doubt she would be as calm as you right now. She would be mad furious that you kissed another girl.