What do I do?

My children’s father and I are *trying* to make things works but he’s just not the most stable person. He’s had all kinds of addiction issues and he has been off of pills for 4 years-or so I thought. This morning he said he was going to try and go to the bathroom. I heard him in there ruffling around with something after about 1-2 minutes he flushes the toilet while sniffing a couple of times. Then when he opens the door I saw he had a folded paper put into his back pocket. Am I wrong for thinking hes on something? I don’t know how to even bring it up without starting a huge fight and him turning it onto me. I need to know because i don’t trust him as it is and I don’t think I want him around my children if he is using drugs. He can be a very mean person under the influence. What do I do?!