Wow, holy shit. That honestly was realistic enough. She basically said she couldn't go out with him because she felt he would hinder her future (regardless of how stupid water polo is as a future). I have to say, well done, I can't believe that he unironically was rejected and it was climactic. It would be kind of souring if he does end up with Hagiwara anyway, almost like a copout. It would also be kind of mediocre to get with Hayami, after stringing her along for so long; I'd feel really bad for her as she could 100% do better.
All in all, this chapter kinda shot this manga's score up for me. It's rare to see a cold hard, honest confession between two relatively realistic characters.