OK, seems like I'm the only person awake (6 hours behind the UK) so I'm going to go ahead and try and offer some advice.
Please don't make any rash decisions. Take a deep breath.
When you think about your future with him, how do you feel? When you think about having babies (if that's what you want) how do you feel? I think there is a definite difference in having someone just grate on your (my DH grates on me all the time but I love him to death) and feeling stone cold panic at marrying someone.
You don't say how old you are? Did you get together when you were very young? Do you feel like you're going through the motions and that you should get married because of the length of time you've been together?
I never had that revelation that my DH was "the one" - all I kept thinking when proposed was that I would love to go to Vegas, just the two of us and get married. In the end, we got married on the beach in Cayman where we live and I had bare feet, pretty low key. All I could think was that the marriage was what I wanted, not the wedding. How would you feel if you didn't have the big day? If it was just you and him somewhere small and personal with a couple of witnesses?
Sometimes the concept of a wedding is so nerve wracking, the worry that the day is all about you and the bigger it is, the more terrifying it is. I know some ladies are complete bridezillas and love that but some of us don't. I know I would have been FAR more nervous if I had a great big formal affair - as it was, we had 60 people at ours and I was wearing the big dress but I couldn't wait to get down the aisle/beach and get married (and get the whole thing over and done with!)
Maybe ask yourself the simplest of questions. How would you feel if it were just the two of you, a registrar and a couple of your best friends? Would you still want to marry him?
If the answer is yes, then try and spend some time together without talking about the wedding and explaining that you're finding it all very overwhelming. Find all those reasons that you fell in love with him in the first place.
If the answer is no, then I would maybe confide in someone you can trust to help you through this. I know if I hadn't wanted to go through with my wedding, my family and friends would have supported me no matter what. There's nothing wrong with coming to this realisation late in the day, it is exceptionally hard when you have a decade of your lives combined together to try and break away from that.
But better to be free and honest with your own life, than living a certain lie that you know will end in divorce.
As it is, I don't think it sounds as if its anything more than cold feet from what you've said. Weddings are the most overwhelming things ever and completely separate from what a marriage actually is. You've essentially been "married" for the last 7 years, you have a life together, and a "wedding" isn't going to change that. A wedding is just a day. Your marriage just gets to carry on after it as you want it to.
I hope you get the answers you're looking for love, I'm coming up to my 2nd wedding anniversary so I'm still a fairly new wife - but I think we are conditioned to believe we should feel a certain way when we get married, that we should still be in a honeymoon period, that we should be overwhelmed with tears like in a crappy romantic movie and there should be fireworks and endless I love yous and boak inducing soppiness. Yes that happens to some (drunk) people but for others it is very simple. You love each other, you want to make it official. I have no unrealistic expectations of my husband but more importantly I don't have unrealistic expectations of myself as a wife.
We don't change, we are exactly the same (only sometimes we get a different name).
Good luck chick