How do you date if PMO has given you a cuck/stag fantasy?

I’m sorry that I can’t answer your question of if it will go away or get better. But I can tell you that I have almost exactly the same story as you. No problems whatsoever with P but when it comes to a partner or even the thought of a partner and myself, I’m useless at the moment. And it is honestly very difficult to date with. I had a girl drive 2 hours for me this past Saturday and couldn’t perform for her which eventually led to a relapse. So in my own personal situation I’ve decided to just not date at all until I’ve at least curbed my appetite for P, at least the more destructive fetishes of P. Instead I’m going to use this time as if I were in prison, only using my time to better myself in every way I can and overcome my demons. The quote, “You can lose a lot of money chasing women, but you’ll never lose women chasing money” is a very good motivator in reducing the importance of dating during these difficult times for myself.
Also, just remind yourself that porn isn’t real. It just isn’t, it’s not in human nature to enjoy being cuckolded and just say it isn’t you, it’s the addiction.

I would actually take comfort though in knowing that your situation isn’t unique and it does seem to be a very common occurrence with PMO addiction, especially with a cuckolding P preference. Just read through the success stories from people who changed their lives through nofap. And I honestly believe that it will fix us. So just give it your best effort, even if it means writing a daily to-do routine for even the most mundane tasks in your day like brushing your teeth or washing your face, as well as time to improve yourself in other ways such as fitness, reading a book and learning something new, meditating, finishing projects you stopped before. Anything to keep your mind busy and give you a sense of accomplishment.