Our dirty little secret (levi x Petra/Rivetra)

Auruo and Petra have been dating ever since their second year when they joined the trainee corps, so they end up going to the same regiment together (survey corps) but what happens when she falls in love with her captain "Levi" and has a secret relationship with him? but most importantly, what will happen if Auruo finds out?

NOTE: there is some lemon up in here