Oxy is VERY Addictive, even for people who have no prior addictive patterns. People get addicted to Oxy all the time from just having them after surgery.
No one with a history of addiction should be taking OXY.
Big clue that this is already a problem. You don't take OXY for a sore back. He didn't get these from a RX. He said he had one, but you found several more.
Please take this serious!