Not sure what to do!?!?

So my boyfriend and I have been together for 2 months today. He was running around and left his phone with me which has no lock and I’ve been told I’m allowed on whenever. So as a joke I go on Snapchat to text his sister a funny text and realise a girls name is on there. So I go onto the chat and read him asking if she was cute and if she could send a picture of herself (as in a selfie not a nude) so he comes over and I confront him. Idk what to do because who asks another girl if they are cute? I mean why would he care or want to know that. He admitted that he thinks it was flirting and didn’t think much of it at the time he asked her. Do you think this is suspicious behaviour and could have lead to something else or possibly still could with someone else?