There are two pairs of characters who are somewhat alike but have opposite fates.
Rosanna and Rachel: Both are intelligent and strong-minded.
Rosanna is plain and deformed, born into wretched circumstances, with no decent road to making her way in the world. She loves Franklin Blake, but can’t even get him to look at her.
Rachel is beautiful, rich, with a loving family. She loves Franklin Blake, and can have him if she chooses.
I wonder how much pity Rachel felt for Rosanna.
Ezra Jennings and Franklin Blake are more alike.
Jennings is an honorable man who has been falsely accused of something, and can’t prove his innocence. He has lost the woman he loves because of this, and his life is blighted.
Blake is honorable and is under suspicion of a crime, which has alienated the woman he loves, but he has the possibility of clearing himself.
I don’t know about the first pair, but I think Collins meant Jennings and Blake to be the opposite sides of the coin. That is why they are so attracted to each other, and sympathetic to each other. Blake sees in Jennings what could happen to him, and Jennings sees a vicarious second chance in Blake.
Why were they attracted to each other before they knew each other’s stories? I’m not sure, though it’s a trick of romantic writers to have instant sympathy between characters who are going to be close. I caught the same homoerotic whiff that Jonathan did, but I have no idea how seriously Collins meant it.