In a happy relationship still dicey about getting married. Any advice

Hello all, I am 26 years old female. I am in a long term relationship of around 5 years with one of my schoolmates. He is a good person. Sometimes he is annoying. Recently I have been listening to Acharya Prashant if anyone of you know him.!! I love the boy very much, am truly dedicated to him both at physical and emotional level. Have no other person in my mind, still when he talks of marriage and kids....I get anxious a little bit. I am dicey about getting married. We both are well settled. We have been the part of each other's growth. We were nothing when we got together, we worked together and got into good positions. Never left each other's side. He says he want to get married in the upcoming two years, but I still feel I am not ready for this marriage thing. I don't know why I feel this but yes I do. Can anyone guide or help me in my feelings.