Please tell me what you think this means?

So, I have known this guy since high school (which is about 10 years now). We dated back in high school and then broke up when we went away to college. We had been on and off throughout the years. We have been on now since January of this year and things are really good however, we are not officially in a relationship. Last night he told me that he thinks we are moving fast because of your history together and etc.

So what does that mean to me? Should I back up off and give him space? If space how much space?

Thanks