Should i tell him his girlfriend is cheating?

this girl i go to college with has been with her boyfriend for two years. he is older and has a bmw and works as a professional golfer. she's been sleeping with this ugly boy in the year bellow us and everyone knows about it, which makes it worse. cos they're together all day they kiss in front of us and hold hands, it's just so disrespectful! i mean, if you're gonna cheat at least be discreet! I feel so bad for her boyfriend cos he worships her, but she obviously has no love/respect for him to cheat so openly- she's even told me she doesn't even love this ugly little boy, even though he's madly in love with her. i know she just loves the attention, so should i tell her boyf?? i think he needs to know!