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Certainly have him neutered first, if he hasn't been. Find a cat behaviorist. And consider medication if that doesn't work.
But sometimes there is no kind way to let an animal live in our world.
I'm a senior volunteer at a no-kill shelter; I work with the dogs, but adopted my own cat there. The terrible secret of no-kill shelters is that it's an impossible goal. Sometimes animals must be euthanized for reasons of physical health, when their quality of life cannot be made tolerable with the full effort of a very good veterinary hospital.
But sometimes a dog--and yes, sometimes a cat--while we work with them to try to socialize them and make them happy and safe to live with, can't adapt. If we have a dog that we realize can't be trusted not to bite, unexpectedly, and through no blame of its own (something in his experience or brain tells him it's the thing to be done, and you can't always even tell if it's nature or nurture): that's a dog we can't adopt out.
And it's true for a cat, too.
Two or three years ago an article in the New Yorker recounted the author's tragic history with a little dog she'd adopted from a rescue. It turned out the rescue knew the dog was unpredictable and dangerous--it seemed to have neurological issues, and would even, horribly, attack itself--but didn't tell her. She, of course, loved the dog, who could be very sweet when not wrestling his demons, and tried everything, absolutely everything, all kinds of trainers, medicines, everything. Even as it injured her, injured visitors, injured her partner.
Whatever had gone wrong in this dog's brain turned out not to be fixable. It was only when she realized the dog was as unhappy, living in what must have been to its perceptions an unrelentingly hostile world, that with much mourning she let it go.
If you end up having to do the same, it's a small, real tragedy; and not your fault. I hate when we lose a dog at our shelter, but I know we do everything we can before concluding the dog can't live happily and safely with humans (and there aren't other options--we used to send some to a very crowded really-truly no-kill shelter but the conditions became too inhumane; see the documentary "Shelter Dogs" for footage of the miserable animals trapped in stereotypic behaviors like eternally pacing in small circles: like that: not an option).
Your cat isn't content and at home in the world. Give him a chance to learn to be. But be prepared to let him go if you have to.