It's never about the reason for breaking up, but the emotions involved that leads to it.

Become deaf to the "words" for a moment, and have a feel for what she was feeling. "Words" are filler for what a female wants to express. Sometimes they make sense, sometimes they don't. But what's important for a guy to get is the emotion behind it.

Now that she's left, you shouldn't chase her but start building your own life. Chasing her is not a masculine trait, it might even make her more repulsed. You need to give her space to wonder about whether she did the right thing. If she is serious about still being with you, she will contact you. Only then do you open up to her. If it takes too long, limit the contact to just once a week.

There are many reasons for why a woman might break up with a man, and it's definitely not as simple as a "petty ultimatum". It's definitely to do with the woman's inner-feelings. It might have been the past - did you show her presence whenever she came to you, or did you just redirect her to whatever you were doing? Did you meet her emotional fixes? Do you live a life with purpose?

Sometimes, if it's really your fault, then you apologize sincerely. But if it's not a mistake, you need to let her see it.

Now she's "guarded". You need to probe her. Ask her, "What's wrong?" And if she replies about the petty remark, you probe her further - "What's really wrong?"

Even if she refuses, you insist. You push on asking, until she gives in to you and tells you really what is wrong with the relationship and what she feels about you. You continue probing, until she says "I'm glad we had this talk, I feel better now."