I loved that scene where he stopped at that spot along the wall where he first saw Chitoge, leaping over it, knee-first. When you have a 'significant event' like that as the introduction of two characters to each other, it's hard to deny they were meant to get entangled and irrevocably change each other. They were meant to be from the very beginning of the story.
But it's still sad that she couldn't stay for the remainder of their third year. But if she found her calling, then that's amazing.
This time... making a promise as someone that is almost an adult, they will hold to their word, and reunite as lovers eventually.