Cheating is generally defined as engaging in romantic or sexual activities with someone other than your partner without their knowledge or consent. The gender of the person involved does not change the fundamental nature of the act.
So, if your wife engages in romantic or sexual activities with another person, regardless of their gender, without your knowledge or consent, it can be considered cheating. Infidelity is about breaking the trust and commitment within a monogamous relationship, regardless of whether the affair involves someone of the same or opposite sex.
It's essential to communicate openly and honestly with your partner about your feelings and boundaries to maintain a healthy and respectful relationship. If you find yourself in such a situation, consider seeking the help of a professional therapist or counselor to address the issues and navigate through them together.