Advice please!!

So me and my bf have been together for almost two years and I’ve been living with him for about 6 months. Today he asked me to message his friend about something while he was driving as I’m doing that he got a message from another female that’s been hidden on fb messenger apparently him and the girl were talking sexually since October (about sending nudes). There are also other females in his inbox with the notifications muted. Wondering if I should just go off or just not say anything. I also noticed I’m not on any of his social media and all photos I tagged him in on fb are not on his page.

Please give me some advice!!!!