How do I tell my FWB I really like him

long story short been FWB with someone over 4 years his in the military we do more then hook up, we have amazing sex I mean AMAZING and It’s becoming more intense and intimate and we are honest with each other! We both said if we slept with someone else we would tell each other guess what for the last 4 years we’ve only slept with each other! I like him more then I should .... do I tell him?