Hi throwawayBPD, welcome to the group

I'll jump right to the point:
my relationship is hell and every single night for over a year we have stayed up until 2-4am (not exaggerating) talking to try and apologize for things I have done wrong.
This can change! This can get better.The process may not be "intuitive" or easy at first, yet if you are willing to try, it doesn't have to be like this any more.
I used to defend myself but that made it worse, so I just listen and agree that I was a vile piece of S###.
I see your willingness to change there -- you noticed that defensiveness wasn't making things better, so you stopped doing that.
Now, you're trying a different approach -- agreeing -- and you're noticing that that also doesn't make things better.
A key part of BPD is that absolutely no amount of us agreeing, placating, assuaging, compromising, wallowing, disappearing as a self, can fill the endless black hole of lack of self and emotional neediness at the core of a pwBPD (person with BPD).
That realization may be frightening at first, yet if we think about it... maybe it can be freeing to know --
there is nothing I can do to change how the pwBPD feels.What you CAN do is work on your own personal boundaries for what kinds of behavior and conversations you allow into your life.
Boundaries aren't ultimatums or threats. It wouldn't, for example, be telling your spouse: "You need to stop belittling me, and I mean it this time, or else!" We don't have control over the words coming out of someone else's mouth.
Boundaries don't require anyone else's agreement, participation, or acknowledgement. We don't have to announce our boundaries verbally.
An example of what would be a boundary could be:
(you start by deciding,
privately and inside yourself, if and/or what level of verbal disparagement you want in your life)
When your spouse starts to tell you "you're awful, you betrayed me, you're the worst, you're literal demon spawn, blah blah blah"
you do not have to stick around for that!You can decide inside yourself "I don't stick around to listen to people verbally abuse me".
And then you might say out loud: "I'm going to take a walk. I'll be back in an hour" or "I need to hang up the phone. I'll talk to you when I get home at 5" or "I'm going to make some juice. Let me know if you want a glass" or something similar.
...
I acknowledge this probably wouldn't be easy at first. There's an existing dynamic in your relationship where he might expect you to stick around and be "the garbage can" for his feelings. So, if you make the first change by not staying to listen to yourself be insulted, he may escalate... at first. Decide if you're ready for that. If so... don't give in, even once! You will be able to make it through. He may in fact, counterintuitively, simmer down after testing that boundary a bit.
There's a lot to unpack in your dynamics, but I really wanted you to know that if you're willing to try some different approaches, your life doesn't have to be like this any more... and it won't take anyone else's cooperation.
Check out the backstories of members 15years, thankful person, and Cat Familiar, for starters -- many aspects of their experiences with PD spouses remind me of yours.
Keep us posted on how you're doing. Glad you found us;
kells76