I'm in agreement with KcaT — the book spent pages on spelling out how there are layers and layers of pretence for each of them. How each is a bundle of keeping others at a careful distance.
I mean, Kanade's feelings about Frederica are pretty plain from her dazedness and — I wouldn't call it jealousy, but disappointment, at seeing Freddie with another girl. And Frederica just stated, flat out, that Kanade's the only person she's been this attracted to. The "until we get bored with each other" bit sounds cold, if you're used to passionate confessions and all-consuming love, but —
It's at the same time a self-aware joke at their studied casualness, a front to keep that casualness going, and — just a bit — Kanade's insecurity and self-doubt.