The accepted version of virgin nowadays is lack of vaginal penetration (at least for hetero sex). However "sex" by definition can mean any type of sex. If you have had oral sex but not penetration, then you have had "sex". If you don't believe me, perform oral sex on someone then ask your significant other if they feel you cheated or not.
RAMA
Then again, if you make out with someone it could be considered cheating, but no one would consider it sex.