The True Definition of Diet.

A diet is merely what you eat on a regular basis. It is not starving yourself, or not eating anything good or tasty. It is only what you decide that you will eat. Eagles have a diet of fish and small animals. Birds have a diet of worms. Cows have a diet of grass. As a person who wants to lose weight and keep the weight off, your main goal is to adopt a diet which will help you do so.
So when you think of diet, do not think of it as not eating or starving yourself. Think of it as what you are going to have your daily meals consist of. That is all that a diet is. That's why so many people fail when they decide to "diet", because in the false use of the word, many have misinterpreted the meaning.
Now that you have decided to lose weight and get in shape. Of course you are going to want to include into your diet only healthy foods. Just remember that a diet does not mean starving yourself. It just refers to what you eat on a regular basis. So make your diet consistent with your goals of getting in shape and staying there.
Just one more point, and this is a good one: If you are having trouble cutting back on the junk food and poor eating habits, maybe you are not as interested in getting in shape like you said you were.