I think that you are absolutely right in your description of the attitudes Harry and his mother need to adopt. I think you are dead wrong when you say it has nothing whatsoever to do with the family next door.
Once an HD person gets rid of their feelings of "emotional fusion" and accepts the fact that cookies = love is not necessarily a law of nature, the fact remains that the HD person still has a sweet tooth. Speaking from my own experience, "differentiation" did nothing to decrease my sex drive, it just allowed me to claim it as my own. Once you claim your sex drive as your own, you are free to consider expressing it in any way that is in line with your integrity. So you will naturally consider whether you might get more or better cookies if you were to let the Mom next door adopt you.
You want your H to choose to love you. The only way he can choose is if he has a choice. Part of having a choice is considering whether soccer and some cookies at home is better than no soccer and lots of cookies next door.
"Tell me, what is it you plan to do with your one wild and precious life?" - Mary Oliver