He is fully devoted to his sister and she dies, then he gets corrupted and starts seeing visions of his sister and since he cares about his sister so much he listens to everything that the hallucination says. Then he creates a massive prison break in the PoE, leaves his former fallen friends and befriends the scorn who look to him as a parent. Uses all of them in some master plan that likely began the moment Mara Sov was presumed dead. Gives up everything and finally opens the gate to the dreaming city only to realize his hallucinations were actually caused by a giant mutant servitor thing that eats him and then later spits him out. Then we shoot him in the head after his corruption was removed and his last thoughts are that he failed to bring his sister back who was still alive but he never knew this, and then he just accepts his death after knowing the wrongs he made. Legit one of the saddest and most tragic stories ever.