I understand what you mean. I didn't like the idea of not being 17 anymore, because I had such a fun time being that age. However, when my birthday actually came I had an awesome time and what i found was best about turning 18 wasn't the actual birthday, as it is with most others, it was what happened after. I found that being able to go out to so many places i hadn't been able to before really changed my mindset on things. I would try not to think of it as a big milestone which everything has to be perfect for, because things never are. What you can instead do is focus on having a good time, don't think so much about the actual day, think about what comes with it and the new opportunities it will bring and try to enjoy them instead of thinking about the things you feel like you're losing. Its not how old you are, its how you feel! I guarantee that the new experiences being 18 can bring will far surpass any negative feelings you had about the day before it happens. I hope that you feel better soon!