Either 1) He is going to propose and wants to keep the element of surprise OR
2) He wants to move forward by moving in/buying a house together without further commitment.
Not really sure if he is playing you along or does indeed have plans to marry you bust just isn't ready yet. However...
If you are ready to get married and he is not then you should probably sit down and have a serious talk about it. And then decide whether you should move on OR you can wait until he is ready? If you wait remember there is a chance that he may find that you are not the one. Personally I would not buy a house together without an engagement. That is kind of a big financial commitment without any real relationship investment.