What counts as cheating in a relationship?

HESOYAM (anyone who gets it, gets it).

Looking up test answers or hacking games is definitely cheating in a different sense!

Wibwob.

It’s cheating when you break the rules you both agreed on or betray trust.

Switching the cookie between hands behind your back after the pick is definitely cheating!

Just wondering… this question is for everyone, men and women alike.