This girl at my school is getting cheated on by her bf of a few years

So these two couples have been dating since 2022. They are basically the hit couple and have lots of love for each other ... thats what some people perceive them to be ... me and the guy are like mutual frens .... and i kw his gf from primary skl but we arent frens .... last year in 12 grade he met new frens mostly girls and about three guys .. him and his gf became frens with the girls and so on they are always together at the lazy bench eating and chatting wen its lunch .. i could sense the shift of energy wen the bf meet these frens.... there was this one time i was passing the lazy bench and heard one of the girls ask another one of the girls if they liked the guy .... i didnt hear all of it cause i walked pass... unpon hearing this i went and ask the guy if he knew that one of the girls liked he said ew and refuse to believe... he still remain frens with them even tho i told him that one of the girls liked him.... these are the same girls who are fren with his gf .. they sit and talked everyday ... without even knowing that these girls wants her man .... i picked up on this energy before her even tho she around them and her bf 24/7 ... to further cofirm what i think i heard one of the guys in the fren group talking about how the girl bf and the girls and some other guy have a group chat and the bf and the guys are sending dick pics for the girls in the group chat to rate how big it is ....mind you these are the same girls that are basically her frens ... anyways i want to tell the gf but am afraid that she is not going to believe me (she is far gone as well as blind to these situation) and i dont want the guy to harass me because he knows that i would be the one to talk and tell his gf and also the girls would probably want to fight me because me and one of the girl have a conflict... he is not treating his gf different tho he buys her anything she wants and treat her good... but he is most definitely cheating with one or more girls... should i not tell her for my own safety and make her find out herself ? Or should i tell her ?