Hi Katerina, so sorry to hear that this has happened to you.
I really hope, for your sake, that you are done. I hope you will write a list our for yourself of why you want this relationship to be over. We can tend to gloss over things after a few days or a week. The brain isn't really happy dwelling on negative emotions, so reminding yourself is a real help. Keep the list really handy, on your phone or in hard copy so you can refer to it anytime you start to romanticize the relationship.
You have done all you can. You asked him to get help, you probably offered other help to get him there, he is not interested, he's not done drugging yet, may never be, that's up to him.
In other words, he doesn't have a problem with being an addict, you do.
Many people idealize the relationship and what it could be. It isn't and it may never be and that should be your focus. There is no magic wand. Let's pretend he was all in for treatment next week and went to rehab. It can then takes months and years for a person to work out all the issues that drove them to drug themselves in the first place and the person that shows up after that may not even be the person you know.
In fact, he started using 3 weeks after you got together, you don't even really know him as sober.
What you do know is that he hurts you, that this relationship is not good for you and that he is just a tornado of drama.
Going no-contact with him right away will allow you time to heal.
I'm glad to hear you are making a therapy appointment. Also, if you are feeling desperate remember there are always walk in clinics, your GP or even the ER.
You have a lot of support here too, of course.