Should I tell my bf to go to rehab or should I just leave?

We’ve been together for 3 years. We live together and he has a 10 y/o son from a previous relationship, who also lives with us. Several times in the first year I found evidence of him abusing (snorting) norcos. I confronted him each time, and eventually I had enough. I broke up with him, and we ended up getting back together a week later. I’m very deeply in love with him, and from the beginning I’ve felt like he’s the one despite all the issues..when we got back together, he quit.

Then a couple weeks ago I saw a norco fall out if his pocket. I didn’t say anything. Then on saturday, when I was putting laundry in the hamper, I noticed he left his money clip (he keeps all his cards and stuff in it, wrapped in a few dollar bills, instead of a wallet) in his pants pocket. I pulled it out and on the bottom of it, in between the dollar bills and cards, there was a short plastic straw caked with white powder residue. I left it untouched so he wouldn’t know I saw it. I got really angry and haven’t talked to him much since that night. I haven’t touched him at all or said I love you, etc. I was waiting until today to talk to him about it because his son goes to his mothers on Tuesdays and Thursdays. So I was waiting for his son to leave to have a talk. He (boyfriend) left for a dr appt awhile ago and will be home in roughly 2 hours.

Since Saturday when I found the straw, I immediately knew I had to break up with him..but now I feel like I’m starting to chicken out..I love him so much and feel like I don’t want to just give up. But then again, we’ve been through this a few times before. Should I give him the ultimatum of “go to rehab, or I’m leaving” or should I just leave? I’m also wondering if I should contact his sister (who lives out of state, but is a doctor). I’m close with his mom but she has a serious problem with overreacting so I don’t want to tell her. I’m afraid that if I leave, he’ll get worse. I’m worried for him and especially his son. Also he will be very angry with me if/when he finds out I told his sister.