Hi OP,
I didn't want your post to go unanswered because you sound so desperate and frustrated.
If you've been dieting for years on and off, you probably know all the 'advice' that people give (move more, eat less), and that really does you know good. Knowing something doesn't make it easy to do.
Have you thought about the fact that maybe it is because of underlying factors that keep you in this unhealthy cycle. I don't know your history, but for many people a bereavement, or childhood trauma, or something like that can be a trigger for them, and they rely on food as an emotional crutch. For others, their low self esteem means they want to put up a physical barrier, a wall against other people, against relationships.
If that's the case (and I'm not saying that it is necessarily), then fad diets and short term calorie controls are not going to work for you. They may work for a while, but you will ultimately end up back where you are, because you are dealing with the symptoms and not the cause.
I would urge you to consider some counselling if you feel that would benefit you, to try and understand why you turn to food for comfort. Talk to your GP, ask for a referral for OA or maybe CBT.
Please don't think this is the point of no return, don't give up on yourself - it is never to late to make changes.