My friend & her cheating boyfriend

My friend just found out her boyfriend cheated on her with his ex. I think she's crazy to stay with him.Is there a polite way to tell her without damaging our friendship?

if yuu guys are truly friends;; Then yuu telling her your oppinion Isnt going to damage anything, She Probly knows it in the back of her head. just talk to her about it and see what happens♥
xx.XX

She needs to learn this life lesson. You should support her decision on whatever she wants to do but you can still throw out the facts to her. I mean if he cheated on her with his ex, he will not doubt go back to her because he wants the best of both worlds.