Dropped the "Prenup" bomb. Now what?

My fiancee and I have been engaged for now a year and 6 months and are less than a month from being united in a civil union/domestic partnership. His parents are currently getting a divorce because his father committed adultery on his mother. Knowing what I know of psychology i know that these things are trendy especially among family. So, I asked if he would be comfortable with setting up a "Prenup" of a sort to protect us both from the possibility of the infidelity of the other. I know it sounds like I'm accusing him of being unfaithful, but it seems only the responsible thing to do as more than 40% of marriages fail. Needless to say, things didn't go well. He feels like I don't trust him. Have i punctured the heart of our relationship, or is there a way to mend things? Anyone been in these shoes?