Talking to each other and getting to know each other. Time spent. Trust earned.

Probably....

Usami san would know....

[And then she felt sad. Would she ever see her again?]

Then what makes each action different from the other? Why is a kiss more than hand holding? Why is sexual intercourse more than a kiss? I thought maybe it was related to emotions.

I'm not very good with this sort of thing.... I don't understand it.