Sooyoung and Jiwoo have been friends for so long, and Sooyoung is scared. She's scared of throwing away their friendship over her feelings, scared of making Jiwoo run away, scared of being rejected. She's not usually like this, but Jiwoo makes her feel this way, makes her nervous and scared and happy. And Sooyoung doesn't want to lose that.
But, after seeing Jiwoo walk into the kitchen in Sooyoung's clothes after sleeping over, Sooyoung thinks it might be worth the risk after all.

or: Sooyoung buys Jiwoo a toothbrush to keep in the bathroom of Sooyoung's apartment.