putting of engagement

This may be a little long so bare with me! My SO and I have been dating for 3 years. During the first 6 months of our relationship everything was perfect. Literally, perfect. He would make comments frequently about marriage and an engagement. For me, this was way too soon to be thinking of these things. A year into our relationship, I was completely on board. We talked about our future kids, planned our wedding (all theoretically of course!) and actually went and tried on rings... Year 2 of our relationship he began to run cold, never wanting to talk about our future, making me feel uncomfortable for bringing it up. We were actually supposed to have our own place this month but he's put his life savings into a new business venture, preventing us from being together properly. Wouldn't have cared if he was still as eager to be my husband but he's always going on about us being young and what his family would think!  Last year he told me, "I think we are still young. Next year". So I've tried to be patient but am I doing something wrong?! A year on and now he's telling me "next year". Both of us are happy being together. I love him and I know he loves me. Things are good in the bed room and our relationship but I can't understand this change in his mind??