From what I can understand with his words, I think he meant that he knows the disparity between his prowess and Tomo's dad's. To say something like "Please wait for the time I can defeat your dad so we can start dating," Jun probably considers it downright selfish because he didn't want to make her keep a promise that has no defined time of conclusion. What if he couldn't defeat her dad for the rest of their high school years? What if he still couldn't defeat her dad when they graduate from college (or even if they can even go to the same college)? Was he selfish enough to make Tomo wait for him?
That's probably what he's thinking, not at all believing that Tomo has waited all this time for him to see her as a romantic interest. She's not about to give up now, and more than that, she's not about to let her dad ruin this chance further now that she already has it in her grasp.
In other words, more cliffhangers are upon us as the arguments and shenanigans mount. Maybe even a training montage. Either way, I'm hoping at least for a satisfying conclusion to it all.