Well to answer why they think the ship sank, aside for Episode 11 (which is not in the novel), Reina confessed to Taki-sensei, but he mistook it as admiration, and Reina took this as a rejection, but Kumiko seems to keep on cheering her on. Shoe1 gave Kumiko the hairpin, as her bday present (in the novel).
And in the novel, after the Nationals Competition, Kumiko realizes her heterosexual feelings for Shoe1 and confesses to him and they become happy together (while Reina stays heartbroken). We're all just somewhat expecting this ending.
Nonetheless, personally, I'm okay with whatever ending as long as Kumiko doesn't end up with the guy. lol