Help my friend 😩

So I have a best friend that is a male .. so hes been in a situation with his baby momma that they are always arguing he doesn’t wanna leave her cause they obviously have a son together lol so we work together we work at night so basically shes home alone at night .. I caught one of my other co workers texting my best friends baby momma so how do I tell him that he’s getting cheated on the go worker be talking About her and the way he expresses himself about her is obvious that something is going on .. how do I tell my best friend or do I tell him he’s a good guy and she has already told him things and done stuff that has made him think she’s cheating and even before I seen her text my coworker 😔🤭 please help I feel so bad but I don’t know what to do