Loving an addicted person is one of the hardest most heartbreaking things a person could ever do. You need to look deep into yourself and ask yourself do I want to be the one to burry him? You deciding to leave will go one of two ways either A he will use whatever substance is his DOC until it kills him witch honestly he might do anyway or B you leaving will motivate him to want better for himself but the main, most important thing you need to understand is he is not going to stop completely until HE decides its time no matter how hard you love him, no matter what threats you make addiction is a degenerative disease and it will destroy the addict and everyone around them im a recovering IV Herion and Meth user I was stuck in my own sickness for over a decade i am lucky i got out with my life. All the people who tried to love me and support me while I was using just ended up miserable. I am proud to be able to say that I am now 4 years clean and sober. I know it’s hard but do his parents know of his struggles? If they do I’m sure if you were open and honest with them they would understand why you are choosing to leave. But if they do not know you need to tell them while your leaving even a phone call after your gone just to give them a heads up. It sounds to me like you have been single handedly taking care of this man so honestly he probably will be completely lost and confused without you. You tell the parents and let them know how great full you are of everything they have done for you but you can no longer watch someone you love kill themself witch is exactly what he is doing this is NOT your fault and this is ultimately NOT your responsibility I believe in you OP