Aww, I really know how you feel! My FI has not only been married before, but he has two kids with his ex wife! So when I was pregnant with our daughter, nothing was really that bigga deal! Going and registering for gifts, I was so excited and he was like "been there, done that!" But he already knew how to be a great dad, so I guess it was a blessing in the end??
As for the wedding, just remember that she is his PAST and you are his future! Clearly things didn't work out and he has found you! He has probably learned a lot about marriage and what doesn't work which might even be helpful for your marriage.
Try your best to make your wedding unique and your own, but don't give up on something you really love and want just because he may have done it at his other wedding! Good luck!