Once a fortnight isn't too bad in the general scheme of things - but I feel your sadness and worry. Coupled with diminishing affection in general, you feel like your relationship may be losing its inner strength?
However ... I also agree with the PP who advised to be careful you're not accidentally turning into a sex pest! If he's feeling insecure or otherwise anxious about some other part of his life, then what he needs from you probably isn't a hand job. How good are you at gently encouraging him to open up? Would he be more relaxed over dinner at a restaurant, on a walk, in the car?
Other than that, porn can definitely put the user off real sex. The mainstream stuff gets more extreme & less humane with each passing year, and of course the algorithms keep pushing towards even harsher content. Knocking one out with your own well-practised hand, while shockingly vivid images barrel into the primal recesses of your brain, has a forceful impact quite different from the messy & squidgy realities of body-to-body sex with a human you care for.
Has the quality or nature of your sexual interactions changed, do you think?
I'm not saying he couldn't be seeing someone else, or thinking about it so much that his mind's already there. Just that it's far from a foregone conclusion.
As usual with relationship issues, the starting point has to be some real talk. Not specifically about your sex life or your feeling of abandonment but where you're at, both individually and together. See how that develops.