*disclaimer: this is only my OPINION and it's OK to not agree with me :) *
From what I've read in your paragraph, you are living a life of stress. When one is constantly in "fight or flight" mode from the stress of a relationship, one cannot make good decisions and can even act like a person they don't recognize. It is clear this relationship has caused much more detriment to you than joy. Your SO doesn't want to change because they don't have to. They know that what consequences for their behavior you will proffer will not last for long. Being ignored is emotional abuse. I people say all the time "but I love them" or "but I was once so happy with them". Because we were raised with the fairy tale nonsense of "love conquers all". NO IT DOES NOT. Not when you live with someone with a substance abuse problem that they refuse to address. Not when you share your finances and life with someone who repeatedly damages both and manipulates you into putting up with it. Most of all, not when you live with someone who is emotionally cruel and completely selfish. The biggest disservice we do to our children is teach them that if you love someone, you put up with horrific things you wouldn't wish on anyone else. No.
I was best friends with my husband for 7 years before we dated and got married. When I walked away from him, I lost everything. I was 100 percent in love with him, plus he was my closest friend. But he refused to take any responsibility for his role in how he treated me. Refused to change, and didn't get counseling until after I left. He went to counseling for 2 years at least, but I resisted getting back with the love of my life because I knew deep down his troubled childhood would never allow him to truly treat a woman well for long. And I was right - his second wife ran away in horror after 7 months of marriage. And good for her I say!
A relationship is more than love. It's a friendship, it's a business partnership, it's a family. If a partner refuses to treat each role (and in the end, you) with the respect and appreciation it deserves, why stay?
Some fear being alone above all else. But being alone has its upsides BIG TIME. You wont instantly be happy being alone, it's something you have to grow into and allow yourself to shed years of conditioning by society (the only path to happiness is being in a couple bullshit) to realize you've been lied to about being alone.
Bottom line: alone, you have hope for a better future. With your current SO, it's clear that after such a long pattern of really horrid behavior, you have very little to no hope for anything getting significantly better. The only "better" you will get is when the SO" is manipulating you into coming back. That's the yo-yo feeling you describe. And the yo-yo feeling is a huge red flag to run as fast as you can the other way.
But of course I don't expect you to take my advice, because if you were ready to do that, you'd be out the door with a lawyer and a restraining order by now, and the door to your heart would be bolted shut against this SO, just to guarantee your survival. You say you still want to salvage things. Others on the outside watching this, if they care for you, must have the sensation of watching a toddler repeatedly put their hands on a hot stove, each time withdrawing a hand that is more damaged and hurt, and then inexplicably, gleefully running back to the stove to get another heapin' helpin' of painful burn. It is not pretty to watch, and even without knowing you I can tell you that you deserve better. But only you can decide if and when you're ready to step away from the stove, get out of the kitchen, and let the burns heal. I wish you the best of luck. In the meantime, consider going to an Al-Anon group (I've heard mixed things), read anything you can about codependency and about living with a narcissist, and also read the book "The Seven Principles for Making Marriage Work" by Dr. John Gottman. You are in the middle of things and cannot be objective - doing your homework might help draw in a bit of balance to the way you view your reality right now. I wish you the best!