Jaime said that he only feels alive when he fights or when he has sex with Cersei. She refused his attempts in the first episode, so he thought that he must force her, just like kings and lords had to use violence and wars to assert their claims. I'm OK with this. There never has been such a thing like "Jaime turns from bad to good guy", just because he got some traumatic events in Season 3 (respectively his events of ASoS). Even if the consensuality might have existed in the books, this deviation does not change anything regarding Jaime's character development. So, this is my first post in this forum and I want to apologize in advance for any grammar error. I'm from Germany and thus there can appear some mistakes.