I think I can help.
You can never truely stop being fat, even if you initially lose the weight.
Losing weight is the process of draining the fat cells in your skin of their contents, but after getting filled the first time, they stay stretched out like an old whore's funhole. Therefore making it much, much easier for them to refill themselves.
And in addition your body becomes used to the amount of heat that the fat in your body once produced, so losing a large amount of weight will make your body temperature drop to a level lower than it's accustomed to, and it'll make you pay for making it slightly uncomfortable.
Plus there's the whole stretched out stomach issue, but I won't get into that because it's common knowledge.
And last but not least are the psychological effects associated with spending your childhood and adolescence with extra weight. Not only will you always believe that you're fat in your subconscious, but the behavior of using food as a means to comfort yourself will always be hardwired into your base instincts.
Fat will get you eventually, it's very, very patient.