Question: what to say to someone that you cheated on?
Answer: Take Responsibility. Admit your cheating. ... 
Have Empathy. Show some understanding for how your actions have effected your partner. ... 
Say That You're Sorry. Express your remorse explicitly. ... 
Ask for Forgiveness. ... 
Make Reparations. ... 
Promise to Never Cheat Again. ... 
Give Them Time to Answer.