My younger sister had the wedding all planned, the honeymoon booked, and a month before, realized it wasn't what she wanted and called the whole thing off.
Ballsy, that sister of mine.
The honeymoon was nonrefundable and already booked - they went and had a great time, and eloped a few months later. (And he's a pretty normal guy - no addictions, not even cold feet - - - it just wasn't what she wanted and she had the guts to do it.) And we were so proud of her.
If you have second thoughts, trust your gut.
The very first second thought I ever had was on my honeymoon. (And this was well before he truly descended into the hell that is alcoholism) We'd been high school sweethearts and together for 4+ years at that point.
(My divorce was mediated and therefore relatively cheap, and the divorce itself ran about 10K. Add another 100K for alimony and it added up...)