William’s / Man in Black’s story is actually really, really tragic and sad.. He fell in love with this girl, Dolores, he thought he saw what she really is, he thought he found something special, and he believed in her! And he had that romantic story with her, that made him lose his mind completely when he lost her..
Than after everything he did to find her, he saw her again, but she didn’t remember him!!! It was like nothing happened, and some other man approached her the way he did.. She was looking at this new man, the same way she looked at William for the first time…. But he kept coming back to her.. WHY?
I believe William was kind of sick before he met Dolores, and he disliked Logan before he met Dolores of course.. but the tragedy of their story and the fact that the only good thing, the only right thing that happened to him, is ONE BIG LIE must hurt him a lot. He probably lost any hope for true love, and he felt like a fool who fell in love with robot?!.. He hated himself because of that. Who knows how many times he killed Dolores and raped Dolores.. He hated the fact that he loved her once.. a robot. He found pleasure in killing her and anyone of her kind.
I believe that everything about her was frustrating for him, and he became obsessed with her and her world. He bought and tried to understand her world, but he couldn’t. He only managed to become crazier than he was..