Should i do this? or is it wrong?

soo i've liked this guy for a reallllllyyy long time. he's on the brink of asking this girl (who I HATE and who is mean and selfish!) to be his girlfriend. it really hurts and I know i could be better to him than she could ever be. is it wrong to send him an anonymous message saying that he should open his eyes and see who's out there because there is someone who is dying to get to know you and the girl you're with is ALL wrong for you? idk...