The climax of the party is that there is an event called "wine glass tower". It is a tradition of the high school that everyone has to drink 4 glasses of wine from the tower. This event was started by the principal when he was a principal here. He was a very wild boy during his youth but when he became the principal. He abandoned all of these antics and became serious.
Each of the glasses is counted according to the people who have accepted the invitation.
This is also the reason Rosalyn has refused to drink any alcohol earlier. She is light-headed and wants to keep herself sober as long as she can. The minute the drinking starts and everyone is going to lose the sense of surroundings.
They have gotten off the dance floor. "I need to go to the bathroom." Caleb kissed her head. "Bathroom is that way." Rosalyn pointed towards it and Caleb went towards it leaving her alone there.