Marbeck, I am really sorry that things are like this for you.
Porn addiction, and all of the associated behaviours, dishonesty, disconnection, loss of self - and the all effects on partners, loss of control, loss of self esteem, hurt, pain. It is all such a harrowing and horrible thing.
My experience is not exactly the same as yours, but I am a partner of a man who is addicted to porn and has been free of porn for 8 months, and I have learnt some things along the way.
Firstly - One of the most valuable pieces of advice I got was from another partner on this forum, they advised that you cannot control what your partner does. You need to put yourself first. That was really hard to swallow at first, but it is so true.
Your partner is going to do what he is going to do. And whether that means he gets better or stays in the mud - you cant make him do either.
I would advise you to research betrayal trauma. A lot of that stuff resonated with me so so much, helped me understand what was happening in my head. Dr Kevin Skinner has some recordings of group therapy sessions on youtube which are really good. There are also a lot of good resources on 'Bloom for women' (lots from Kevin Skinner who is really great).
A lot of that will tell you this, but I would really corroborate the fact that it is really good to find someone/ people to talk to, to work out a safe place in your head and to seek some counselling yourself. All of these things helped me hugely.
Second, I would say boundaries are so important. And the important thing here is that these are boundaries for you.
For instance one of my boundaries are that I wont tolerate any porn use/associated behaviour (because my partner was sex chatting and messaging lots of people). Now I know that this is different in your case because you partner hasn't stopped yet. However, why I'm using this example is the way this boundary works for us. My partner is free to make the choice to use Porn/associated behaviours, I cant control that. But I wont be in a relationship with someone who does that, so I will leave the relationship if he does.
Not me telling him what to do, me controlling my environment, if that makes sense?
Sure these things arent always black and white. Perhaps after having a good recovery effort I might be able to stay and support him if he had a slip and was honest straight away. Those are more personal decisions. But again, I think it important that you make those decisions based on your needs, not his.
You will need to consider what boundaries you need for you.
Other examples of boundaries include, 'you've lied to me I now dont feel emotionally safe with you and I wont sleep in the same bed as someone I dont feel safe with so alternative arrangements need to be made.'
The important thing here is that you are taking back some control of an issue in your relationship that has taken so much power away from you.
Of course, boundaries are hard and I appreciate this is a difficult thing to do.
Also, the other side of not being able to control others is that he might not be able to adhere to your boundaries, which might mean the relationship does not work for the both of you. That is always an option that is hard but has to be faced - from what you wrote it sounds like you have already faced this fact.
I would definitely advocate for the benefit of counselling. My partner has done this and it has been very helpful for him and there is a clear difference in his ability to talk through things now. It is important to find the right fit, but addiction is also tricky and people will often use different excuses to avoid addressing it. Perhaps agree a timescale together?
Lastly, because this is an essay now - I would highly recommend the book 'love you, hate porn' and if you and your partner were in a place to be able to read it together - perhaps you arent in the place now, but some time - it gave me and my partner so so many tools on communication which I honestly believe has been one of the biggest keys to us being able to navigate the last 8 months.
Also, I suggest some research into porn addiction - 'your brain on porn' is a good book, it will help you to understand some of what is happening for him. I think being part of his recovery journey, if you feel able to is a really good thing, and the change of language to a more hopeful one might also help. But I would say - prioritise your own support first. I did a bit too much focussing on his addiction in the beginning, to the detriment of looking after myself.
I hope this is helpful. As I have said, our circumstances are different but if anything helps it is worth it