She is so sad when you always ignore her and not put attention on her, so she tries to make you jealous, she lies and tells you that she is cheating, but in fact she is an innocent girl and never tries to cheat

"I have been cheating on you! HAHAHA, it's because u never pay attention to me, i find another handsome boy who can love me more!"

(in her mind: lying successful, i hope u mad!)