Does a fuel relay slowly go bad or is it all at once?

It will go bad suddenly. If the fuel pump is running, which you can tell by listening at the fuel filler with the cap off and a helper turning on the ignition without starting the engine, then the relay is good. If you hear nothing then either the pump or relay is bad or you have a blown fuse. If you hear nothing check the fuse first. If it is good replace the relay. If it still does not run the pump is bad. Even if the pump is running that does not mean it is good. It may be running but not pumping any fuel. A fuel pressure test will verify the pump's condition. Be sure and replace the fuel filter either way.