I am kind of struggling with the same thing myself. I understand what addiction is, I grew up around it, I was stupid enough to fall in love with an addict, but then again, who I loved then and who I am with now are definitely not the same person. He looks the same, but he's not. And it helps me knowing that he knows that he is falling apart. He knows that he is not the same person right now. He doesn't even like himself, so it helps when he says all that manipulative stuff to me.
Anyway. I am learning that addicts really do live in their own delusional world. And they can sit there all day and say they need help, but it's one thing to talk and another to actually do it. I used to think like you-if he loved me, he would stop. But really, it is a totally separate thing now. I do think he loves me somewhere VERY deep inside, I do think he knows that he has lost me, maybe forever this time, I do think he does want to change. But it's not enough. Addicts have to actually want to stop drinking or drugging or whatever. They have to think that is their only choice to change, or else.
Every bottom is different for every addict. You see addicts who lose everything and they still don't care. You see addicts who stop for no good reason (that was me-I never hit a bottom, I just woke up and said I didn't want to do it anymore, and I haven't since). It's different for everyone. But you can't go down with him.
And if you said you are going to leave him, do it. It doesn't have to be forever, but he needs to change, because his current behavior is not acceptable to you. You have to focus on yourself, or you will be just as bad mentally as he is. TRUST ME.