Yes, you have to talk to him, find out the story. He did not have to do it that way, could have used cash or otherwise "hidden" what he did but he didn't, perhaps he wanted you to find it. He could be very conflicted so I would think about what you want and how you feel and know what is what with yourself and then see what is up with him and his thoughts about where to go from here. Then decide what is best for yourself and child in this situation. If he is using again, he needs to get help now and you cannot stay so close or you could be sucked in and taken down with him (not into drugs but into lies, deceit, arguing, etc.) and that would not be good.

If $140 is a lot to you and you were stretched thin this month, it does not sound like he was doing drugs as they would cost more? I would take to him immediately and try to head off whatever problems you can before they get worse.