Help! *drug related*

So I was at my boyfriends place last night and he said we should go back to my place but he has to go and pick his mate up and drop him to town. He asked to use my phone to text his mate as his is broken I was laying next to him and he swiped across and I seen all these messages saying he'll come over and have a few cones and bring the left overs from last night. (He didn't know I saw that) he then made me leave his house before him and he went back inside and got his drugs (once again doesn't know I knew) he took 2 hours to drop his friend off and when he finally got home went to the bathroom (didn't know I could see him) and put his head under the tap and washed his mouth out and then ate a whole bag of lollies. When I asked what took him so long he said his mates were there and talking to him he told me the address he was going to but I know he lied about it because he knows I don't like the friend he was going to smoke cones with. I told him at the start of the relationship drugs were a deal breaker for me only to find out last night that he's been lying to my face for 2 years. I want to get some kind of evidence before I confront him please help! (Sorry it's long)