Leo's advice ⤵
First and foremost, I am so glad you've noticed that it isn't healthy for you. The answer to the question depends on how he affects you when he's not on his best behavior, and according to what you've written, he's affecting you in a negative way and right now at this stage of life, you need only positive vibes around you. You stated that you've already tried to get through him but it hasn't worked. I believe the cause for this might be his use of drugs because it takes a toll on a person and changes them for the worse at times. Before I give you my advice, just know that it's not your duty to take care of him, you don't HAVE to help him, it's totally fine if you don't because at the end of the day he's not your responsibility. My advice to you would be if you truly have the patience and feel as though you should give it another try at helping him, then go ahead but if it fails again, you should slowly try to distance yourself from him. Focus on your well-being first.

Summer's advice ⤵
I'll start off by saying that, you seem like a very sweet and intelligent person. I think it says a lot that you've realized that perhaps a relationship like this isn't exactly what you want or need. But obviously you still care for him and you're torn between staying or leaving. The question is whether or not he really needa help and whether or not you're willing to be that person to metaphorically put your heart out there to help him get through it. The risk is rather huge and the mere fact that he may not even need help is a red flag already. I think you need space first and foremost. I think you need time to be yourself and time to heal and grow once more. You have feelings for him and in some way you want what's best for him but he may not see it like that. So, you need space and peace within yourself before you start thinking about him. I'm not telling you to back, I'm just saying that you need space to really think about what this relationship is about.

Lime's advice ⤵
Although we don't know the reason for his behavior, cheating and drugs are never the right solution; not only does it harm the both of you, you may end up with serious consequences. I know you have a very precious and kind heart, thus you may want to help him become a better person, but changing someone is not an easy task. If you're really willing to help him, I suggest for you to bring him to some proper counselling and understand why he may have drifted into doing drugs. If he doesn't wish to get therapy, I would strongly recommend you to leave him. You have a bright future waiting ahead of you, and it's not worth it to risk it all just for someone else. In the end, your happiness is the first priority and I hope you may live on peacefully without such worries.

Nicole's advice ⤵
You honestly don't need someone like that in your life. He decided to make the wrong choices and continuously has shown you that he won't be changing anytime soon considering he went back to his old ways. I love that you're passionate about changing him and all but you should do what's best for you and walk away because he has already chosen his own path. You're a junior now, you should be focusing on your future and not worrying about the negative vibes he's giving you like Leo said. Cheating is also something you shouldn't condone with. I bet you're an amazing, beautiful and nice girl and you deserve more than someone who'll it up, someone who chooses drugs instead of you. Your best chance of helping him is offering actual help and he doesn't take it then you shouldn't be worried, If he is willing to change for the better and wants actual help then offer it. In this situation, you come first. I wish you the best of luck, sweetheart.

Sabby's advice ⤵
I think you should just let him go. It's good that you're aware that this is not healthy for you, but you keep forgiving him anyway and that's not right. You shouldn't let other people see you as a push-over and treat you badly because you will eventually end up regretting it later on in life. Maybe it will be difficult to let go of him, but it needs to be done because from how it sounds like to me, he doesn't seem like a very caring and loyal person, given the fact that he has cheated on you before. Plus, if he's a generally stubborn person, then you won't be getting anywhere with trying to change him. You deserve somebody better than him, somebody who will truly love you and cherish you. And you will find that person one day. But for now, you need to leave this guy, since he clearly doesn't see your worth. I hope this helped. :).