Cheating on your girl is the worst thing you could ever do to her..
you mentally f/ck her up for the rest of her life, and you ruin her self esteem. She'll do everything she can to be "skinny" "beautiful" or "perfect" just so you can love her again. Go into extremes like starving herself or wear tons of makeup to feel pretty. She'll push everyone away. She's gonna be afraid to trust anyone again. Let boys use and abuse her because she thinks she deserves it. She'll go into depression and become someone she said she'd never become. Maybe you don't see it now... But you ruined her future.