What everyone else has said echoes for me too. I am 56 now and have dieted all my life right up to the point where I was edging towards 20st. Some of that was under the drs advice, some on my own. I've learnt that if I try to 'diet' I become obsessed with eating and my poison of choice is very carby. I think changes for me started when I did an online mindful eating course, which was unsuccessful in many ways, but got through to my head to not continually be guilty about eating and to give myself permission to eat what I chose to. Now that might sound like a bad idea, but it made me stop dieting, and strangely I began to lose weight.
Then I found this site and was introduced to the idea that I'm carb intolerant. I started a low carb lifestyle and slowly continued to lose weight. I'm not dieting. I'm eating things I like with the understanding that if I chose to eat carbs then I'm actively harming my health, like smoking. I'm not perfect. I do eat carbs, but I try for the most part to have many days where I eat nice things, that I regard as treats, but which are not carbs. I like bacon, cheese, pork scratchings, nuts, tuna, eggs. I have to watch the protein intake, but I try to keep a good eye on my blood sugars.
My aim is not dieting, but keeping my blood sugars in a good range. I have lost nearly 5 stone though, but very, very slowly - none of that massive low carb weight loss came my way! But hey, I'm not knocking this weight loss as it means I can now walk the dogs without a walking stick and with no pain.
So, I know it all makes you sad and being unhealthy is very depressing, but you can do this. You need to be kind to yourself, find low carb things you like to eat and talk to the very nice and knowledgeable folks on this website. Look at the threads in the low carb forum to get ideas for tasty meals. Maybe at the start think about posting a daily or weekly blog on here. You'll get lots of support.
Take care and best wishes. x