Fwb zone

So I’ve been friends with a guy who was my ex-roommate for 2 years. We’re pretty good friends and used to hangout together frequently. 4 months ago we started sleeping together and fooling around. Im really attracted to him physically but I don’t really want anything serious right now. A few days ago when we’re together he confessed that he loves me and is serious about me. I started crying because I felt guilty of leading him on and using him. I told him the same but he doesn’t believe me. How can I tell him that I don’t see him that way? He’s one my closest friends and I don’t wanna lose him.