Well, the vague ending in the actual panels is disappointing, but if you read the character background pages, it makes things perfectly clear. In particular, the last two bullet points on the page for Tsukasa:
"It must have been hard on her to be the center of two love triangles."
and
"Despite how it ended, Tsukasa will also end up happy eventually. I feel that she's a girl who doesn't think something along the lines of "unrequited love = unhappiness".
That says to me that the other four ended up as couples and Tsukasa is the hypotenuse in both love triangles. Or perhaps the center of the love hourglass? Given that she did seem to be actually impacted by Asakura's confession, having her end up as bisexual in the end isn't a stretch, either. I would have preferred if, when Kotooka asked about her boyfriend it turned out she had a new GIRLFRIEND instead, but hadn't told her two friends that the person she was dating was female yet. (On the flash forward thing where they're meeting in the diner.) But, then again, it would have been better, over all, if the series had gone longer and not ended so abruptly.