Maybe it's just me, but I can't understand the drama behind the whole "should I go to my dream school or be in the same school as the person I'm going out with" that's so prevalent in high school romance manga. We're in the age of technology, and there are people who are in relationships with those across the planet. Heck, even if they were living on the opposite ends of the country, Japan is only slightly smaller than California, so if they really wanted to, they can see each other on the weekends. Take advantage of that stellar public transport. What, do they want to share their school life experience with each other? That's fair, but it's just as fun sharing new stories the other person wasn't there to experience first hand. Fear of cheating? I doubt either of them would do that, but thinking in-universe, if either of them did do that, then their relationship wasn't going to work out anyways
Besides, if they were really so committed to each other that they were willing to consider their future together first before their own future, then they can stand to be apart for 4 years and then spend the rest of their lives together