Masturbation or self pleasure as I call it has been a topic of discussion for many years. Why? Well for starters several of us have been taught it is unhealthy, it is a sin, and it isn't natural. I mean who determines what is natural or not? Is it society? Is it or beliefs? Is it religion? My thoughts are this self pleasure is a healthy way for you to know yourself intimately. By learning yourself and what you like sexually is educating both you and our partner.
We know that self pleasure is a solo journey however is it considered cheating in a relationship?
My thoughts "NO" it isn't. Clearly you aren't having sex with another person. The definition of cheating is: Infidelity is a violation of a couple's emotional and/or sexual exclusivity that commonly results in feelings of anger, sexual jealousy, and rivalry. What constitutes infidelity depends on expectations within the relationship. In marital relationships, exclusivity is commonly assumed.
So by those terms masturbation is not cheating.
If you think your partner is cheating well that is a different story and you should talk about it. As far as each of you enjoying yourself solo sexually can be pleasure for both parties involved. Consider mutual masturbation and learn about each other while learning about yourselves.
Remember enjoy each other and enjoy yourself. Embrace the art of self pleasure.