How do I send my boyfriend to rehab for drug abuse?

He is 19 and I’ve asked him to stop smoking pot over and over, he promised he wouldn’t and now admits he still does anyways. He claims that it’s all my fault started anyways because his first time was with me. He took it too far, and I got disgusted with it(and seeing him under the influence) and quit forever myself quite some time ago. His mother hates that he does drugs and blames me. She doesn’t know that I’ve quit a long time ago though. I hate it just as much as she does. Can I get him to go to a rehab so he is not allowed to get high? I asked him already and he said no though.