relationship advice

My boyfriend and I have been dating for a while. He's a US Navy sailor and he's been talking to me about getting married and living together and things had been going so well. he proposed on Saturday and his mom called him to tell him she wanted to talk about things. I've been freaking out today because he hasn't really talked to me about what they were talking about. The only thing he said that it was about the marriage and she thinks it's too soon but that him and I would talk about it later. I'm scared because he promised that nothing would change his mind about marrying me (a lot of people are telling us that we're too young) and I'm just really scared he changed his mind two days after proposing. I'm so sad and I've been crying all day. I don't know what to do.