prenuptial agreements

My boyfriend and I live together we have been together almost 4 years and recently I found out he comes from a lot money.  Abd recently he came Into even more when his grand parents passsed away who I loved and cared for as if they were my own. I get a feeling he hasnot proposed because his mother wants me to sign a pre-nup and he knows I am very agsinst it!!  Also his mother doesn't think I good enough for her son because I do t come from money but I work very hard for everything I have.  I was raised to love people for who they are not what they have! But I love him and want to marry him. What do I do?