Proposal

My boyfriend has been dropping signs about proposing soon, we are both almost 20 years old, and have been dating for 1 1/2 years. We have talked about marriage, and about him proposing within the the next year. I love him so much! The only problem is that my grandparents (who I grew up with after my mom passed away) don’t like him. They don’t like he because I didn’t go on an lds mission, and they think it’s his fault. ( it’s not, I made that decision on my own) I have told them this multiple times, but they don’t care. I don’t know what to do. I want them to be happy for us when it happens, but I don’t know how. They think we won’t last even dating.