what should i do?

So i have been dating this guy for almost 6 months now.During our first week of dating i searched through is phone and found a girl that has sent him a nude picture ( of her ass) but at the time when i checked the date of the picture it was prior to us officially dating i got mad because he lied to me...he told me he was not intimately talking to no one at the time so i was a bit disappointed but end up forgiving him just less then 2 weeks ago i found out he was back talking to her they did a videocall with each other but did not message each other so i am not sure what they could be talking about. What should i do? let it go and let them be friends or tell him i am not comfortable with them being friends?