need guidance ladies

Which was saved to his phone in March. Ive seen this girl on his Facebook and new exactly who it was, so I asked him about it when we got in the car. He said she's his friend and has low self esteem and one day was talking about how she was feeling herself and sent him a picture so he told her she looked pretty because she was "fishing for a complement". I let it all go, but tonight I got curious while at work and started snooping. I though the girl was around my age maybe a little older but no! She just turned 16!!! He will be 30 before she is 17..: I want to know how and when they met and the dynamic of this friendship both past and present but I don't want to start anything with him because I'm not mad I just want to know. 

UPDATE: I asked him if he knew how old she was and when and how they met. He met her when he was away for work before we met and he didn't find out how old she was until after they hung out. I told him the friendship made me uncomfortable so he deleted her number and removed her from Snapchat. So I think we're good now.