What should i do? My boyfriend of 5 years is not ready for marriage?

well for starters...me and my boyfriend have been together for 5 years. We almost never fight. My problem is that he is not interstate in marriage, sometimes doesn't even want to talk about it! I have set myself to believe that the reason he doesn't want to get married is because he is no longer in love and just used to "us." I have been think so mcuh about this, and i'm thinking of just leaving him and move on. I know it sounds crazy but it feels horrible that after all this time the tought of marriage is not even on his mind. I have talked to him about it, but i didn't want to get to much into detail because i simply don't want him to think i am desperate. Should i continue like this or have some time off?