When my ex cheated, I pulled those exact same cards in a self-reading. The deck was basically spelling it out for me.
The Moon especially kept appearing in every spread I did during that time. I also kept getting Three of Swords reversed and Five of Cups - they seem to pop up a lot in cheating situations.
About the ethics thing - I think it’s fine if you’re reading for the person asking. Just don’t go snooping on the potential cheater without their permission.