He accepted the fact that her tone was maybe a bit snitty - she had a right to be. Hell, they might not have been 'dating', but they had spent time together (mostly in bed, and mostly arguing when not in bed) and he had just ... dropped this out of the blue.
"I'm not - Jessica I assure you I didn't wake up this morning and think that I was over this thing with you." No, he had looked at some old family photos and come to that realization. He didn't want to play the it's not you it is me card, but it was. "It's just - your you. And I'm me, and we want vastly different things in our lives." So that basically was it's not you it's me, but just worded a bit differently.