Bastian already has feelings in the novel but Odette betrayed Bastian by giving his secret/plans towards his father. Since Odette betrayed Bastian he wants his revenge by her giving birth/forcing her. Odette has miscarriage because of Bastian step mom, Odette lost his child and his dog. She leaves Bastian and went into hiding. Then Bastian search for her and wanna ask for her forgiveness/repentance for his wrong doing. (They did the bombayah during Bastian's visit) Then he went to war. Odette confess to him first through letter. She thought Bastian was dead.
It was because Bastian told Odette (when he was torturing her) that he will seek his revenge (for betraying him) by making her pregnant, remove her (Odette) rights as a mother to their child, and he (Bastian) will raise the child with Sardines. This obviously never happened tho because Odette had a miscarriage. However, even if she never had a miscarriage, his revenge plan will never happen. Why? Because he already cut ties with Sardines before he even knew about Odette's pregnancy and he was already planning to live peacefully with Odette which he plans to do after his (Bastian) revenge to his father.
Don’t get me wrong, I don’t like Bastian either, I think he’s a toxic piece of trash too. BUT for a character with so much inner monologue - too many people don’t even make an attempt to understand his actions and end up feeling angry at him all the time.
Bastian is a bastard, but he’s not a character who is just a villain for the sake of being a villain, he’s not inherently evil. Weirdly, his fucked up actions have a reason behind them, and if you understand the emotion he feels and how he expresses this emotion in such a twisted way, it becomes interesting to watch. A dive into a psyche of a child who’s upbringing turned him into someone with emotional intelligence of a monster. And I think in order to enjoy reading this, a reader needs to try to understand him. Otherwise you are just watching a bad guy doing bad things and I can see how it’s not enjoyable.
Then again, I’m only speaking for a manhwa so far in which he didn’t do anything that atrocious yet. But if you’re a novel reader I guess it’s fair for you to hate him from the get go considering some spoilers I have read……