First figure out what is bothering you because this can impact the stability of the relationship. When you are sure you want a bigger commitment, then approach this subject as you would any serious discussion. Sit down and let him know that you are in need of a more permanent commitment. Don't give him the "my clock is ticking" and you have to do it right now. Let him know that you just want to know that the commitment is coming and the date is something that can wait. If you ask him with the understanding that this is a process then he may be more open. If not then he can tell you how he feels about commitment and why. It is okay to want to know where this is going.
If this has been helpful press accept