Re: My ex is being cheated on
If you think that by telling her you're being the good guy that's saving her....you're not. Not only will you associate yourself in her eyes as "The guy who told her", but you'll be having everyone wonder why you even bothered to get into her business. You aren't that close.
She's a big girl and can handle herself. She has close friends and family to help her through this so it's not your place. People get cheated on all the time. Doesn't give us the right to just jump into their business. Just make sure your the guy that becomes her escape. So when she finds out and breaks up with him, you'll be the guy to help her forget her troubles and have fun with her by NOT reminding her of her ex.
"All things are subject to interpretation. Whichever interpretation prevails at a given time is a function of power and not truth."