It seems that that quote about betrayal is the focus point of the whole series. In K1, both Revan and Bastila betrayed others. Revan betrayed Malak and the rest of the Sith, and Bastila betrayed Revan and the rest of the Jedi. In K2, Kreia and Atris both betrayed others, both the Exile. Also, it is shown that the Jedi Counsel betrayed the Exile in the past, and Kreia's apprentices betrayed her in the past also.
It is my theory that there will again be two betrayers, one light side and one dark side, in K3. It seems to follow the tradition that they have set up. It probably won't be your mentor, since that has already been done twice. Maybe your whole party will turn against you, and some main character who you are an enemy of, who seems to be the game's boss, becomes an ally.