Ah, one of those "Wait until graduation" type stories. I'm actually surprised he managed to hold back for 2 years when most protagonist would have just...went for it.
The wait must have made the payoff all the more worth it though, I guess?
Apparently, "Sensei" demonstrated (like the song said): 'more discipline than a Shaolin Monk" ... and for a girl as cute as Yuuka is, it was TOTALLY WORTH IT!