Should my boyfriend know about what I did, when we weren't together?

My boyfriend and I were together and broke it off and about 7months later we got back together. during those months i met someone ,not serious but we dated and had . Well when my boyfirend and I started talking again and got back together ... I never told him about that incident. I dont know if im just emotional today but I feel he should know... should he?? I mean we've been having issues lately already....but do you think that i should tell him, and risk losing him? I know it would seem to be a betrayal to him because I kept it from him