OP, in my opinion, there is something pathetic about playing Sherlock Holmes in a relationship. When you are reduced to snooping, it is time to be upfront about what you have done, and how you are interpreting what you have seen.
Flirty is one of those things that can be in the eye of the beholder, but having seen something ,you should now say something.
If you do not want to be with a man that you think is cheating , you should make that clear. On the other hand , if he is not cheating, he may not want to be with a partner who snoops.
Whatever the resolution, it can only happen when you speak up. You are in a marriage; you are not in an evidentiary hearing. You do not need to sneak around looking for more evidence. No one is going to ask you to produce evidence.
If you want to play games, it seems to me that you can only further cheapen whatever relationship that you have He may or may not tell the truth , but that is always a possibility. Act in your own best interest because once you tell him your suspicions, he will certainly act in his best interest.