Don't dispair, there's a brilliant line in the film Bridesmaids, "You are your problem but you are also your solution'. Only you can decide to conquer this and only you can make yourself do it. You need to make up your mind but, more importantly, you need to tell your mind what it is you have decided. The mind is a funny old thing, it likes it's habits (it takes 21 days to create a habit) and you need to really hammer home what it is you really want. It often gets misguided, it thinks you want the chocolate for comfort so it gives you signal 'eat chocolate', it doesn't realise that it is eating the chocolate that is making you unhappy, it's catch 22.
Just trying to think differently sounds easy but when push comes to shove the comfort zone kicks in and we revert to norm. Firstly stop dieting, your thoughts will always be concerned with food, you'll think about the foods you like then want to eat them. Try to concentrate on being healthy and active, think about how you can do this. Is your true happiness on the plate or can you look beyond it, take a few seconds each time you have to decide on what to eat and ask your self what it is you really want. Affirmations are a good way, keep them positive and in the present tense, maybe "I am dedicated to living a healthy and active life". Repeat it to your self, write it down and read it.
You need to deal with the part of you who who is allergic to the thought of loosing weight, try this. Give it a name and a separate persona then write him/her a goodbye letter. The letter should be positive, do not apportion blame, it was a two way street. Thank him/her for being in your life, make it clear that you both recognise that the time has come to part. Outline your plans for the future, talk about being healthy and active, tell him/her what you will do when when you reach your goal, will you have one big goal or split it into smaller ones. Once you have everything out destroy the paper, if you have used a computer, delete the file from the folder and also delete it from the trash, as you delete it concentrate on the separation and try to feel it leaving you.
Another good way is to keep a gratitude diary, keep a notebook and pen by your bed and write about only positive things, these could be thoughts, events or wishes, it should be in the present tense so wishes must be written about as if they have happened, such as 'thank you for my fortune'.
Good luck and don't loose heart, you are not alone, we are all here to help you.