Can you write down some pros and cons? It might help to get things out on paper? Why are you marrying your DF? Why shouldn't you? Are the cons things you can work through, or are they deal-breakers? Because I think it's better to deal-break before saying 'I do' - but I also reckon most people get cold feet at one stage or another - it's an enormous thing you're doing, to make the covenant to spend your lives together, so I think it's encouraging that the cold feet indicate that you're thinking about all this, you have an idea (well, as much as anyone can) about this great adventure you're getting into.
I know about the 'what if's', and the cold feet - but I know that there's no such thing as 'Mr Right' - just 'Mr Right for Me'.

Wishing you all the best as you work through it all. xo