I'm sorry but a lot of that is complete b****x. He could not have known whom he was better off with. Dorcas did not allow him to get to know his father.
He struggled with the decision to leave Sydney with Dorcas, but thought that he needed a woman's touch. He told Sydney that he would make sure that Dorcas knew where to contact him.
He left because she made it very clear that she wanted nothing to do with him, and so that she had a clear run to look after Sydney. He did what he thought was right for the child, not what he wanted.
I still think that Dorcas overstepped the mark, and that she should have made more effort to help Sydney build a relationship with his father, instead of taking over.