This is often super difficult to do, and the Seinfeld "off like a bandaid" approach is probably best. By doing it clearly and quickly, you allow yourself to focus on what you really want and not to carry around a lot of baggage. For example, I've been approached by previous employers about working for them again and I've had to tell them politely that it's never going to happen. Usually I try to give them some constructive criticism if they are able to receive it, but I admit to having done the "It's not you, it's me" routine before. Basically, I think it's important to focus on explaining that the paths are different and that each party needs to concentrate on their own path without needing to try to drag the other along. A couple of times I've received the, "But I've changed..." thing and I just have to reply, "That's great. I know you'll be able to find great people to work with because of that. I need to focus on my own stuff."