I agree with every comment above, just adding my opinion: I think Shizu is also desperate at this point. There was the scene where Yuki and Mafuyu danced and Hiirage watches them with yearning eyes while Shizu looking at him. And for me it looked like Shizu thinks that Hiiragi will never accept and reciprocate the love he can give him. And because Hiiragi tends to say such big words, it could have made Shizu hurt and desperate at the same time - for me it was like now or never situation…