I'm going to keep this really brief. It'll be like pulling off a Band-Aid… it's not going to be fun but you need to hear it…
Why is it so hard to lose fat and so easy to gain it back. It's pretty simple actually… you have fat cells that essentially store your body fat. When you diet you are emptying those cells but not destroying them. So when you go off your diet all your body needs to do is simply refill the cells, which is very easy to do. To make matters worse it is also very easy to create more new fat cells. So basically this is a huge kick in the balls (or ovaries for you females).
Will these fat cells ever disappear? Yes, but it takes about 10 years for your body to decide it no longer needs them and then destroys them. So you need to hold those bastards empty for a long time in order for the cells to die.
But that shouldn't be your concern for now… finding a diet that you can work with, and getting better at dieting should be your top priorities. Once you master your diet and get your weight to where you want you can start rebuilding your metabolism so that it's easier to hold those cells empty.
The point is you are in control. The path is there for you to follow and it can be done.