Yeah, I also hate it when characters change abruptly (it happens in a lot of games unfortunately). I think he becomes more static as the game goes on though, but I would have to replay it to find out though. He never does hypnotize the friendly childhood friend as she was already corrupt enough for him to do anything with her, but he hypnotizes everyone else. At this point in the game, it is just a lot of breeding and pregnancy sex, but there is some plot left.
Impregnation/pregnancy is done fairly well in this game, which is why I enjoy it a lot.