If I cheat someone, what does that say about my relationship with him or her?

Romans 13:9-10The commandments say, “You must not commit adultery. You must not murder. You must not steal. You must not covet.” These—and other such commandments—are summed up in this one commandment: “Love your neighbor as yourself.” Love does no wrong to others, so love fulfills the requirements of God’s law.

Cheating is evidence that you do not love or respect the person you cheated, and you are thinking only of yourself.