I have been in this situation more than once, and I promise you that the likelihood of it turning into more is slim to none. Sure, he may like you, be attracted to you, enjoy the sex and your company but nothing keeps a man from being with a woman he really wants to be with. You have given him access to the most precious part of yourself and why would he do more to keep that since its readily available? If you are okay with casual, which you obviously are not, then carry on. Since what you really want is a relationship then it is better to cut your ties now to save more heartache and embarassment in the future. You will deeply regret it. Best wishes.