It sounds like this relationship was a deep source of love for you. It’s very, very difficult when you’ve bonded with someone, to come to terms with it when addiction rears it’s ugly head. It’s like invasion of the body snatchers. And you just want the person you knew and loved back. Very painful stuff here
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I’ve been in this position myself, and I know no one wants to hear this, but when you are in a situation like this, it’s an uphill battle trying to get better yourself, when you’re constantly being triggered by, and focused on, the person that is the source of your trigger. Everyone tells you to walk away, and talks about self love, but it’s so hard when even though you might know logically that it’s true, but at the same time you’re in this pit of pain that at times feels like death.
The thing is, it really is a vicious, ugly cycle. And I didn’t like this either, but when you finally face what you are feeling and experiencing when on the receiving end of behavior like this, at some point you just have to ask yourself, what can you do? I have found myself, I do find truth that putting down the person and walking away, not exposing yourself to any triggers (social media, contact with the person, etc), getting counseling (and that can be listening to podcasts, self help/ psychologists on YouTube who you find helpful, library books, group help, DBT & CBT therapist..whatever works for you), trying to keep a routine with meals and exercise, etc are all things that you can do.
Keeping contact with the person and getting triggered over & over is not going to get you the person you knew back, all it does put you in harms way. Good luck, you never know how strong you really are until find that you really can follow through on being true to yourself, honor your own feelings and experiences, and keep yourself safe and out of harm’s way of this shi**y behavior.