Making it work in the long term

All diets work in the short term. Low-fat calorie counting, Atkins, Weight Watchers, The Cabbage Soup diet, they all work.. until they don’t. For a while it’s all roses and you lose some weight.. but then the diet stops working or you start straying and you stop losing and stall until finally you gain it back (and if you’re unlucky you gain it back plus a bit more). See even if you don’t stray.. even if you’re being super strict about it.. eventually all the diets stop working. Or at least that’s my experience so far.

The holy grail then is not really the losing of the weight.. it’s the keeping it off (and to keep losing after the first 6 months).

This I believe:
Your body has a setpoint (the amount and fullness of adipose your hypothalamus has decided you need to have). The longer you’re at a higher weight the harder your body tries to stick to that setpoint.
Insulin cause you to gain weight.
Food causes insulin.
Lowering your calories can cause you to lose weight right up until the point where your body slows down your metabolism (feel tired, feel cold, etc) to the new lower calorie level.
Raising your calorie output (exercise) can cause you to lose weight right up until your body lowers your metabolism and lowers you other energy output (less fidgeting, feel tired, etc).

So I guess my question that I need to figure out is how do I continue to lose weight after 6 months and once that’s done, how do I prevent it from creeping back on.

The two things I currently don’t get are “how do I move my setpoint” and “how do I keep my metabolism high while still dropping weight”.

Cutting calories (by whatever method) works until your body lowers your metabolism (you’re cold, you’re tired, you’re gaining weight even at a calorie level which is much lower than your maintenance level).
Some sources suggest cycling your calories (one week at maintenance, one week at deficit to keep your metabolism revved)
Some sources suggest intermittant fasting (24-36 hour fasts interspersed into maintenance level eating)

Both of these ideas require more research.