I don’t think using sex toys in a relationship is cheating tbh.
Open communication is key.
If my partner told me upfront that they want to use a vibrator, I’d personally be fine with that. But if they did it secretly, it would call into question our entire history. A good relationship is built on trust and an honest representation of each person’s Elo rating.
They should make chess piece shaped butt plugs. Some pieces are just perfect like the bishop.