So Watanuki is mentally recounting that it is probably very lucky that he managed to switch places with Himawari, as this prevented them from being alone together unsupervised in the student council room.
In the translation I’m reading he really makes a point of how two people alone in the student council room is absolutely a potentially romantic thing.
And, I point out, this is as he openly stares at Doumeki.
Who he is alone with.
In the Student Council Room.
And Doumeki just.
Stares him dead in the eyes.
And slowly eats his small french cake.
CLAMP know what they’re doing.