She neglected him though, which is a form of abuse and she basically had Dietrich raise him
He's the equivalent of a rape child, she just didn't want to abort him. Her not forming a bond with the child at first falls under post partum and the fact that she left him to a close friend that treated him well isn't that bad given the circumstances. You have to keep in mind the story. We're not just discussing "whether neglect is bad", it's a specific story where she falls pregnant during the period of time where she's being deceived by him, it's a long process of him convincing her to love him despite her own conflictions with their original relationship. They only finally have sex recently when he helps her fulfill her revenge and then she learns that over that entire time he'd been manipulating her to like the worst degree possible. He tried to kill Dietrich to remove the "love" spot that was already filled in her life, to leave it vacant and take it after convincing her not to look at him as just a boy. He also did it because he was jealous that she gave Dietrich a cloth too, hence him going and taking it and then keeping it the whole time. He then played pillar of support for her in her grief, even though he's the reason her reality was shattered...
This all almost went perfect to plan. He just got caught because Dietrich didn't actually die and a loose end started blabbing about how the possessions were found, unlike he'd been claiming the whole time. There's a common trend here in the comments of people genuinely just... Not grasping who Wilhelm is as a character. The parts where he just stares at people with crazy eyes is the truth, the rest is a facade. He is crazy. Rein goes crazy for revenge, but the rest isn't a facade. She does still care for the people around her. Wilhelm didn't care about Dietrich
I honestly don’t care about their relationship anymore, they are both toxic to each other. But saying that oh she left the child with a close friend isn’t bad, is crazy. The child doesn’t understand why his mother doesn’t want him. He just wants to be around his mom and she is openly rejecting him and then offering him to Wilhelm (like an object) knowing that Wilhelm is not stable enough to be a father.
Is the abuse revealed later? She just said he's never been hurt and her inner thoughts seem to confirm that. It looks like she took care of him as long as she could, but over time couldn't handle how much he was like his father growing up and then Dietrich stepped in to take care of him.