I think if we saw some of those 3 months where Ami was being ignored and getting the cold shoulder from Rei it would make this a bit more satisfying. Since we're just told it happened, we don't get the uh... "Satisfaction" of seeing that kind of "justice"(?) happen to her. But we're just told that it happened due to time (space?) limit and it can feel unsatisfying in that regard.
But I think it's told its story well. Ami has few moments when she starts realizing things and she has real issues expressing herself which outside of her "shitty" behavior is the other issue that leads to that breakup moment at the amusement park. Again, if we saw more of those 3 months it would be way better.