I don't care how much they loved each other, Anne and Frederick only knew each other for a few months eight years ago. No doubt if Frederick had not come into contact again with Anne at Upper Cross this would be a story about a man who found someone else to love after he had his heart broken. He had no intention of seeking her out when he came ashore. Therefore, while Frederick knew that Anne was his ideal, he was content to find someone who had her good qualities; he didn't feel the need to have her.

It's clear that he still feels wounded by Anne, which shows the strength of their attachment, but if Frederick had found Anne as changed mentally as she was physically he would probably be thankful that he didn't marry her.

The point is, I think, that at this point in the story Frederick doesn't know Anne well enough to want to be with her again. He doesn't know how much she has changed (or not changed) on the inside.