Pimafix works for what its meant for. As for fish herpes, gross!
Once a fish gets sick like this, he will never full recover (unless its an African lol). I've had a couple bettas with velvet, ick and all that nasty shit that hits them all at once. They get healthy, but never fully recovered before dying unexpectedly.
I don't think you sound heartless, a fish is a fish. It's smart to cull when needed, especially to protect the rest of the tankmates.
Is he stressed out by the other fish at all? Does he flash on a certain object? Is the tank overstocked? etc etc