If your boyfriend is really sweet like you say do him right and tell him so he can find someone who deserves to be with him! You have already ruined any chance of having a good solid relationship with him anyways. Everything going forward would just be based on a lie and good, honest and respectful people deserve better then that. If you are trying to justify it, because the other guy had a big cock and the sex was better then you don't deserve to have this guy stand by your side and are not ready to be in a commited relationship.
Love may not be enough, but sex? The guy you cheated with...i guess he knew you had a steady? You crossed the line...perhaps a bigger cock works for you...i hope you find a loyal one...let your boring little cock guy go! Jees! Shallow or what...grow up!