we were broken up for a month. i had casual sex with a friend during that month. is that cheating?

david and i were broken up for a month because he was constantly angry and never was around for me. during that period i had casual sex with a friend. then david and i managed to talk our previous problems out and decided to get back together. i came clean and told him the truth. and i have been the best gf i can be since then. its been 8 months since that and he constantly uses this against me. was what i did cheating? should i keep being in this relationship?