It's not anxiety, I can't get it to work by myself unless I have a very erotic fantasy going on in my mind. I have tried no nudity but still naughty videos and that works but that seemed like the wrong direction even if less erotic.
Understood, so there's no anxiety about it not working, but you still would like to change it.
The thing is, that even if it's a fantasy that you create yourself or a form of external source like a video or pictures, what is happening in your brain and body is the result of a deeply rooted dopamine pathway, sort of, essentially you have fallen into a deep trench where the behavior is only available through that one avenue, and all other pathways are so unused that they seem inaccesible.
From my humble view I could suggest a few ideas.
The first is the recognition that even if it's a self generated fantasy, it still is a form of stimulation to get something going. And that works like caffeine would, and if so, the way to recover some of the natural pathways of motivation is similar to quitting caffeine, you could train yourself to not indulge so much on the fantasy world or on the videos for your source of stimulation. As such, you could potentially go through a withdrawal period, but once you've cleaned yourself from it, things should start flowing more naturally.
The thing with sexual energy or desire is that it's always there, and it will find a way to express itself, if you've given it decades of training of only finding expression through a single door, then that's where it'll go by default, but if that door is closed, it'll give you the chance to create a different pathway for it to show through. Though it can be difficult and even painful, but I think it's worth it.
The trouble is that, just like with any other stimulant, overt fantasizing or dissociation, have a way to build tolerance in us, and as such the requirement for stimulation to get at that same level grows higher and higher. So, the way out of it is to consciously spend more time away from fantasizing, and detox from it if you will.
The other thing I was thinking about while reading you is that, maybe as a background to the above work, you could mediate on what you express through sexual experience? I don't think you need to be explicit or descriptive here, or even answer that question for others if you're not comfortable, but your fantasies bring you to a place that expreses more than just the physical sensation, there might be something else.
It could be affection, care, intimacy. But there's a lot more that can be expressed this way, anger, fears, insecurities, possession or submission and so on. So, perhaps this is a great opportunity for you to choose what gets expressed via physical intimacy, which means working on expressing the rest of those aspects in an appropriate manner.
This way you can place things where they belong and give each its due.
In short, the only way I see of changing that behavioral pattern is to look at it from the point of view of diet, you consume something that has had an effect on you, and the way to address it is by becoming conscious of what you consume and quitting it, not without a way to supplement what that was fulfilling. Go through the detox and withdrawal, and slowly come out of it on the other side.
I hope it helps, I know that this topic is as particular as there are people on earth, but the pattern of stimulants and behavior seems to be very similar for most of us.