Don't feel bad. I have the EXACT same problem. When I screw up, I just feel like I blew my ENTIRE diet and gained back everything..I still need to lose about 30 more pounds and I feel like I'm doing just enough to maintain. I remember, I saw a user say...either on this forum or on another forum that "to maintain is as much a victory as a loss at this point" (talking about her weight). And I tell you, I really am happy just to eat enough to maintain because that is what I am doing rather than eating less. But I'm working on it. Of course, if you can eat enough to maintain also, that would be a victory for you too. It helps me to know that I'm not a "failure" because if I am, then so is many many other people roaming this forum because I know they're all where I am at or at least have been there. So don't feel like you have failed, you're definitely not the only one.
I even posted a thread about messing up my diet, everyone had very encouraging words. I think you should check it out, really it helps me to read it when I need some encouragement.
Also, I can identify with the feeling sick and ugly part. I know you have completed highschool, but I am in highschool. And it's not any easier than from when you were here. I just thought this the other day when I overate (accident or not? hmm) I just looked, and thought "You really hate yourself don't you" to myself. I am learning by watching someone else that no one will love you if you don't love yourself. I see this at school with a particular girl..I won't go into the story..but she tries very hard to be friends with girls that are mean to hear. And I see now that, she is surrendering herself and not loving herself, and because of it...no one else will and I find myself thinking how unattractive it is. And then I realize, it's true..no one will love you if you don't. I know you didn't say that your problem is that no one loves you, but my point is that you need to start loving yourself and stop hating you. Just really think how silly it is for human beings to hate themselves. It's counterproductive. When people see you hating yourself, it really looks silly. So you seriously need to stop, and start looking at yourself and thinking about how all the people that have existed in history from the beginning until now, there has never been anyone exactly like you. That's a quote from somewhere...but you understand.
In any case, I mostly snack because I love food and I'm bored. I'm not gonna say "find a hobby" because, well..you can still eat food while doing that hobby. All I can say is, eat the little that you need at one point and then do something else and try not to think about the food. I don't have much advice for that, I'm sorry..I'm working on it myself, I'm trying to keep myself busy and just not think about it.
I hope your diet goes well for you in the long run. And you always have this place to lean on when you can't stand up by yourself!!
Our greatest glory is not in never falling but in rising every time we fall.