The best thing is to follow the golden rule and treat others how you would like to be treated. How would you feel if your partner received cunnilingus from someone else or simply made out with another person while you are together. Cheating is going against the established or conventional rules. If sex outside of the relationship hasn’t already been established between partners, its safe to say that you would be cheating by conventional norms. Communication is key. Only you and your partner have the real answer to the question.