Gut feeling

So for a while my husband has been “working out” and he would come home as if he did NOTHING at the gym. I asked if he was really working out because the time that he did go to the gym he would come home sweating and ready to take a shower. My gut was telling me he was being sneaky. So I looked in his phone (I just had to see what was going on) and I found out that he wasn’t going to the gym. He was smoking weed with his friends. He knows how much I hate it and he promised me 3 years ago that he stopped. How should I tell him that I know what he’s been doing