Has he been health checked? Blood panel done? Urinalysis? If he is not feeling well that may be why he is spraying and not social with your other cats. There are a lot of things that can be done for this cat besides euthanizing. You could consider building him his own little shelter/enclosure in your backyard.
My advice would be to get the cat neutered if your vet feels he is still able to reproduce. It's a pretty simple procedure. The last thing we need if you opt to let him go is more cats around if he is indeed intact. There are millions of cats being killed yearly because there are no homes for them now.
