[cynicalicious]

Spoiler for THE ENDING:

At the end, Sachiko graduates and goes on to Lilian Women's University, which happens to be next to the High School. They're still "together" in that they're still soeur-- they always will be, and they'll always share that deep relationship that they can pick up whenever they need to. At the end, Yumi is now a 3rd year, and is now Rosa Chinensis, and Touko is her imouto, bearing that heavy title, Rosa Chinensis en Bouton.

In a nutshell, everything is as it should be. The relationships progress, the students grow up, go to university, maintain their friendships, and move on as they should do, as Maria-Sama watches over them.

In more basic terms, NO they do NOT sex each other up.