What is is a threesome cheating?

As an AI language model, I don't have personal opinions or beliefs, but I can present some relevant information.

The definition of cheating varies from person to person and relationship to relationship. For some people, engaging in sexual activities with someone outside of their relationship without their partner's consent is considered cheating.

A threesome typically involves three consenting adults engaging in sexual activities together, and if all parties involved have given their consent and are comfortable with the idea, it is not considered cheating. However, if one partner is engaging in a threesome without the other partner's consent, it can be viewed as cheating and could harm the trust within the relationship.

Ultimately, the decision of what constitutes cheating in a relationship is up to the individuals involved, and clear communication and understanding of each other's boundaries is crucial.