Helen The flashback in the final episode (plus previous scenes) suggested to me that the babysitter wanted sex with him. But as she was underage and he was that much older, it would be regarded as rape in the eyes of the law. He may have been guilty of grooming her, though I'm not sure that was portrayed.
The flashback scene to the sounds of the rape in the trailer was awful, and made worse by the partner listening to it outside. The actress who played that victim was brilliant- very powerful and emotive performance, I thought.
Like others, I got the impression that Marie slept with the partner mainly in the hope that it would help persuade him to speak out. She urged him to be honest in court about what he had heard when he was outside the trailer. That he then lied to protect his own reputation was just horrendous. He was quite likeable earlier in the series but he came out very badly at the end.
My impression of Dee and her problems was not that she herself had been abused; rather that she was a product of dysfunctional parents. A religious and emotionally cold mother who she didn't relate to; and a father who she was much closer to, and possibly hero-worshipped, but who was profoundly flawed. And she had witnessed what happened with the babysitter, which would have been very disturbing.
The babysitter bullied her- making her smoke, and mocking her when she got her period. Very odd dynamic between them.
Although Paul was not brought to justice for the rapes, I thought he got his worst nightmare of a punishment- losing Marie. Convincing the jury that he hadn't done it is one thing; but in the end he couldn't convince his wife, who knows him better than anybody. He looked terrified when he realised she'd gone. The party and all the back-slapping and congratulations became meaningless if she had gone, because despite his fucking awful behaviour over so many years, he really loved her, and knew he couldn't function without her.