You are not a failure. This happens to EVERYONE! Cravings are normal.
I am quite slim for my height (between 7 and 7.5 stone, and 5'2") and I crave things every day. I am a chocoholic - I think about it all the time and I have to really work at making sure I don't go overboard.
However, occasionally I don't have the energy or wherewithal to be strong about it and I end up eating a crap load of chocolate
Just yesterday in fact, I was fed up and frustrated about work stuff and throughout the day I ended up eating about 3 and a half chocolate bars, around 300 cals each, plus breakfast, lunch and dinner and some fruit in between. I wouldn't normally allow myself to eat that much chocolate, I try to have just one treat a day.
But... I'm not going to dwell on it now, because that was yesterday. I felt a bit bad about it at the end of the day, but I told myself, "It's okay. Maybe I needed that today. I don't do it every day and I won't do it tomorrow".
Today has been a better day eating wise - not as good as I usually am, but better than yesterday, and I haven't had chocolate. Tomorrow I will try to do even better. Tonight I'm going to do my Zumba to make up for it a little, which I happen to love (even though it's an effort to get started).
The key thing to do is NEVER WRIGHT YOURSELF OFF! Don't give up! This is a life long journey. Life is a long time! Are you going to have perfect healthy eating days every day from now on until you die? Of course not! You wouldn't be human. There are going to be days or even weeks where you can't get a hold on your eating, that's just something you'll have to accept. Providing you keep on keeping on - exercising, finding new motivation, taking little steps throughout each day to choose something good instead of eating something rubbish, you WILL get there in the end. So long as the majority of your diet is healthy and consistent.
I think it's good to have little goals along the way, but they shouldn't be the be all and end all. They are there to motivate you, don't make them so big that you feel like throwing the whole thing away when you don't make it.
People look at me and presume that because I am slim I can eat whatever I want and that food isn't important to me. I am ALWAYS thinking about my next meal!!! Even when I'm eating my breakfast I'm wondering how long it is 'till lunch

I appreciate it's easier for me because when I have a bad eating day, I don't look in the mirror and instantly think "FAILURE". I imagine that if you already feel fat, it's harder to get the motivation because the end results seems too far away and you can't see the point. Everyone on this forum, especially in the Before and After section is living proof that if you don't give up, you will see the difference.
I hope no one thinks I mention being slim in a boastful way. I only mention it as a way of explaining that anyone can have overwhelming cravings, and that in itself doesn't make you a failure.
If food is a priority for you, that's a good thing because it means you care about it enough to make smart choices. Most of the time
Disclaimer: I write too much. Please don't sue.