Remember, people who are tortured by guilt are easily manipulated. Derek is the way he is now because he is trying to make up for losing Yvonne or evening going to the market in the first place, in his mind its easier to blame the "Villainess" than face his own guilt and thus falling deeper into the brainwashing pit making it harder to fight back even if he wants to. Still though you can't help but feel a bit of resentment towards him.
Remember, people who are tortured by guilt are easily manipulated.
Derek is the way he is now because he is trying to make up for losing Yvonne or evening going to the market in the first place, in his mind its easier to blame the "Villainess" than face his own guilt and thus falling deeper into the brainwashing pit making it harder to fight back even if he wants to.
Still though you can't help but feel a bit of resentment towards him.