My goodness, Amasato-chan was quite the Assertive type of girl. As for male protag-kun (don't recall his name being given), his earnestness just might cause her to fall for him.
Perhaps months or years later, the synchronous and spontaneous crying out ("God Dammit All!!!") will be looked at fondly as their mutual mating call, which was answered in rather spectacular fashion.
Ah, when two people who are very much alike just to happen to curse the couples around them at the same time, that is how true love is born.
So she had someone she liked but someone beat her to it, and he confessed a lot but kept getting shot down. In a way, they're licking each other's wounds, but sweet Vanilla can still be born from that!
Great ending, though. "Don't go getting all serious before I do", eh? I interpret that as a good sign for their relationship going forward, really.