You may be feeling this way for various reasons. You've mentioned fear of commitment; other may be- you have become to feel stagnant in this relationship, your expectations may have changed now that you know him better, you do not want to be someone's step mother, trust issues, you may be stressed out about- finances, employment, etc.
Try to jot down an inventory of possibilities and then meditate over each of the possibilities. Your intuition is trying to show you something (whether it is about you, him or the relationship itself)
Taking some time off of the relationship is not a bad idea (if you believe that it would be helpful to both of you. Hopefully he understands your needs)