You have to break up with Nicolas because your father and Nicolas' mother got married and you became half-siblings. On the other side, you feel happy because you can live at home with Nicolas, but on the other side, you are also sad because you have to be your half-brother.

"It's okay for us to be half-siblings, but we can share love like brother and sister, right? means I can hug you without worrying that our father will be angry." with a slightly tease tone and grins.