LauriandVic's advice seems excellent to me. I feel things can't always be ideal. You can't demand perfection from the other person, because everybody has flaws, and it's not always so romantic. It's important not to base marriage just on your own selfish wants. But all relationships are happier and more fulfilling if you compromise and strive to understand and forgive the other person, and are charitable towards them not because they always deserve it but because you love them. I'm young, but my relationship with my fiance has grown and matured a lot over the past four years because of the things I've mentioned.
I was never engaged before my fiance, so I don't know how much this means, but this is my gut feeling: If you're suddenly scared about not being single anymore (because of loss of identity, etc), anxious about some of your fiance's minor flaws (which can suddenly seem important with a wedding approaching), or wondering about unknown relationships you'll never get to have, I think it's probably jitters. If there's an issue inherent in your relationship that makes you unhappy, and you're proceeding because of the excitement of a wedding or because you're just so used to having been with the person for years, you might have a deeper problem.
Do you love him? Is he good to you? Are you compatible? Are you marrying into a healthy, practical situation? Or does he make you unhappy? Do you feel pressured to get married?
Future Mrs. Joseph Mizzi