Don't give up yet and you'll win. Your H has thought through for so long and he does not make decision. I don't think he wants to leave at all. Unless you give him a new reason to. It is not easy to leave a M after twenty odd years. He said that his A has ended last year. Why should he start now if it did not work out by then. If jealousy can help your cause, do it. But I am not certain. It depends on your H's character also.
In my case it is more complicated as my W can't think straight because of her depression. SHe does not trust me either. That is the difficult part. Unless she trust me and want me to help her, it is very difficult for her to open up to me. What can I do to help her trust me? Be her friend?