Cravings are a natural part of addiction. Withdrawal is very real. Good job on making it to a month, that's solid progress. I've found that relapse tends to happen when you let your guard down. For me, physical exercise is key to staying sober, but it isn't always convenient or easy to stick with a routine. But when I do, cravings are reduced and I feel 10x better as a whole. Exercising releases dopamine and other chemicals that make the brain happy, like a natural antidepressant.
Above all, remember that when cravings hit, it's your brain trying to draw you back in. You don't want porn, you want to be rid of it. Your brain creates powerful feelings and illusions to lure you back. Stress can also be a factor. When you feel stressed or depressed, your brain starts craving happy chemicals even more. SO if you have a bad day, be extra vigilant. Keep telling yourself that it's all in your head, because it is and you can overcome it.
As some have stated, relapses make your brain weaker and more susceptible to more relapses, much how eating a single potato chip often leads to ten more. But the metaphorical bag of chips here is endless and the metaphorical chips are much more unhealthy. One relapse can't undo all the progress you've made in a month, you brain HAS recovered a decent degree. But your progress is dependent on your ability to rebound. You will be weak, disoriented, and vulnerable after a relapse. You will want to give in again. Focus on getting your head back on straight and moving forward. Avoid relapse like the plague because if you don't, God only knows how long it'll be before you're able to go another month. Good luck.