Hey, consider yourself lucky he only has ONE ex.
Don't let this spoil your wedding, it's really silly. This is just nerves and a little insecurity rearing its ugly head. You said yourself he's a lovely guy, so don't worry about it. Him having been with another person before you were married (or even together) has no effect on his feelings for you or your future together. Consider yourself the one that 'won'.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi