“I know he has had previous relationships with women and they have been sexual. I contacted his ex to find out if she had any similiar issues (I know that was wrong). She told me that the sex was the only thing that kept them together for the first year.”

Is it possible that the fact it was sex which kept his previous relationship together scared your current partner, and that he would prefer his future relationships to move more slowly?

People can be intimate in so many different ways, and perhaps he wants to make sure there is a better basis for future relationships in the hope they last longer?