Yeah even Donna at times had to tell him how he was treating her was wrong. He took out a lot of his anger on her when all she wanted to know was what was making him so upset. They never would have worked he never fully trusted her especially after finding out about her cheating on her fiancé with him, also both of their competitive natures. I personally wanted to see Harvey with Donna but Harvey and Scottie could have also been great if he opened up to her. Overall in the end I don’t think Harvey has had a better sexual connection with anyone else in the way he had it with scottie and he definitely cared about her and had love for her but he wasn’t in love with her. I think she finally realised that and that’s why she turned him down in season 5.