What should I do?

Tonight I found a condom in my hubby's book bag that he carries to and from work. I don't know what to think or do. I haven't said anything to him yet because he is playing video games with my brother in law. 
I wasn't snooping before any says why was I in his thing. Once a week I go in his bag and clean it out. He tends to leave lunch containers in it so I get them out so I can wash them. Well tonight I was pulling stuff out and seen a gold wrapper on the bottom so I pulled it out. I am furious right now but am not sure how to go about it. 
I can't even figure out how he would cheat. I drop him off and pick him up. He works with my uncle so if my uncle seen something funny he would look out for me and tell me. 
How should I approach my hubby?