Need some quick advice

Rach • Mommy to a 7yo 👧🏼 and new born 👶🏼 boy

So my fiance asked me message someone for him (buying stuff for my daughter off fb) on his phone. I don't ever go through his phone or anything ever, like never our entire relationship except in the beginning when he didn't trust me and we switched phones. Well he has been glued to his phone. messaging people and he told me it was his buddy he hadn't talked to. alright, cool glade your talking to your friends. But how slow he responded made me skeptical plus he hasn't been leaving his phone around. So I snooped a little and feel a little bad until I see 2 chicks in there. one I knew for a fact he was FWB before we got together the other I didn't until I clicked and saw exactly the shit I didn't. another chick he use to be FWB with, these girls are gross like nasty, we are from a small town. everyone knows everyone. one of them even tried to use my daughter to flirt with him. his response was well she isn't mine. like wtf you are the one who wants to adopt her and marry me what you talking to these nasty chicks For? I have not said a word to him because I know I have to be calmed down but how the heck do I go about this?