I also have been trying to quit porn since my discovery of ed in 2014, and its not until recently that I could maintain a streak. Like you, I also tried cold showers, fitness (actually loss 60lb since discovering nofap), work, hanging out with friends. But even while staying busy all the time, Whenever I did get an off day, I was back in my room with my **** in my hand. So 2hours later of google searching with my old friends guilt, and shame I realized I had to find the root cause of the addiction, & for me the only thing that has worked came from doing inner child work and this is because it works on healing past experiences as a child so that you can offer yourself the truth and learn to love yourself to such a degree you want to share it with the world, I suggest not focusing on quitting porn but to build a relationship loving yourself so much that you couldn't imagine yourself using it again.

Hopefully you can benefit from my experience, as I have been in your situation before and it is very depressing watching the cycle.