CB,
Congratulations on reaching 51 days. I hope to be that far in someday soon, but for now I've only reached 10.
I've been hit with a lot of anxiety as well. This in part comes (at least in my case) from the fact that we can use pornography (or any addiction) as an emotional crutch to deal with stress and difficult emotions, which turns porn use into our default coping response. Also, addiction is a disease that affects our brain, and one of the fundamental brain changes that occurs in addicts is a malfunctioning stress system. What this means is that when we come into contact with a stressor, our body responds with a more exaggerated response than normal, sending our stress system into overdrive and inducing many withdrawal symptoms (including anxiety). I understand that even if we are aware of this, it doesn't make the anxiety disappear. I really wish it did. But hopefully this information provides you with some solace, that is assuming you didn't know it already.
I noticed you mentioned a few times that you felt more cravings after having sex with your partner. Have you ever heard of the chaser effect? After we orgasm, porn addicts may have intense cravings. So you might want to consider avoiding orgasm (either from sex or masturbation without porn) for a longer period to give your brain time to recover. If you still still want to have sex, there is a technique out there called Karezza that allows you to do so without orgasming. Please check it out if you're interested.
Lastly, I think it is important to remember that addiction revolves around dopamine. By fantasizing or looking at images on the internet (not necessarily pornographic, scantily clad women or just women that you find attractive can lead to this as well), we are actually creating spurts of dopamine within us that activate our porn-conditioned circuitry and impede the progress of recovery. I am only ten days in, going through one of the most difficult periods of my life (lots of external stressors), but I have miraculously been able to push past all the obstacles (urges, withdrawals, desensitization) so far, completely PMO free, and I think that this is thanks to the fact that I have been on monk mode (i.e. no fantasy, avoiding any intentional peeks at content that I could perceive as sexually stimulating) almost the entire time. I am still early in my recovery, but I think I feel more recovered compared to my past streaks.
Sorry if my response was a bit long, but I have read and watched a lot on this subject over the past year, and I just wanted to share something that could potentially be helpful to you on your journey.
Wishing you all the best, I am really glad to hear you have a supportive partner. Keep up the good fight!