Hi Jg and welcome, sorry for what brings you here, of course.
Perhaps it's time to start focusing more on yourself and what you want in your life and less about him? He has made it clear what he wants (drugs), what do you want?
That is not to discount your relationship, I'm sure he as good points too or you wouldn't have stayed with him. He is a liar and a cheater and an addict though, those are the facts, are these things you want in a partner? I know they are not (who would!).
The truth is you didn't Cause it, can't Control it and can't Cure it (the 3 c's). He will quit drugging when he is good and ready and not one moment before that. You can't help him with that, it takes a strong commitment from him and some help, preferably good solid professional help as well as something like AA or NA. Doesn't sound like he is there, at all, as he said.
There is a book that is very often recommended here, Codependent no More by Melody Beattie. I hope you will grab a copy. I'm not saying you are codependent or not btw, it's a term that is used too often in my opinion but there is a wealth of information in the book on things like our own boundaries and relationships which you might be able to relate to.
In the meantime, please try to focus on yourself, what you want and need in your life is important. Al Anon (for friends and families of alcoholics) or Nar Anon, might be helpful to you too. I know right now that Al Anon is running online meetings.
https://al-anon.org/al-anon-meetings...onic-meetings/
Addiction is addiction so don't hesitate to join Al anon if you like, you will be welcomed.
You might also find some current threads in the Friends and Family of Alcoholics forum, which tends to be more active than this forum, of course feel free to post over there as well anytime.
https://www.soberrecovery.com/forums...ly-alcoholics/