L.M.
I don't see an issue with it. My husband and I did not have any assets when we got married so it was not an issue. It certainly doesn't sound like he is trying to make it financially difficult for you to get out of the relationship or anything like that, he just wants to be careful.
I know that the process and the idea of it stinks, but if you think of a marrage as a legal union between two people, it sounds like you have the type of fiance that likes to dot the i's and cross the t's on that contract. Nothing wrong with being overly cautious and, in a way, I think it shows how serious he takes that union.