if he says he will - then try let him at it...
I am sorry but I have to say this.
I think that you are relying on this too much. I think you just have to be happy with each other and whatever happens will happen. You can discuss your future with him and see what he thinks but I think it's strange that you have a date set and no proposal. I was with my H2B longer before he proposed. You just have to let it happen and not push it. Unless you propose yourself. The more pressure that you put on him, the less he will want to do it.
By setting a date, has he not already proved to you that he is commited to you and the relationship? Do all of your family know that you have set a date?
I can understand that you want to make it official but did you not discuss this before you set the actual wedding date? I don't understand how you can set a date but not officially be engaged IYKWIM..