Being an adult changes things.

You have a job, you have friends, you have your own flat. You're finally in control of your own life and no-one can tell you what to do. You don't have to constantly be on your toes. You can do whatever you like - and eat whatever you like.
Then you realize you've let yourself go. The skirt that was a little too big a year ago is suddenly almost too small. There are parts of your body that you wouldn't even look at if you had the choice. But somehow you can't stop looking. And you make a decision.
Because you can make your own decisions now. You can eat whatever you like... or choose not to eat whenever you like.
Your boyfriend wouldn't be happy about it and you know that. He thinks you look good in your British size 8. He wants you healthy and feminine. He knows your little secret (and you can't help but think that perhaps you shouldn't have told him). But he won't find out. You'll make sure he won't.
After all, you know how to lie. You went through it before, only then, over 10 years ago, it was harder. Deep down inside you knew that it will catch up with you eventually. You knew it from the start.