WOW - sorry to say - but it does look like it went from "weeping" to "dying". When you break a piece of the branch, is it dry and brittle? Did you see any worms (like May saw worm) or caterpillars (like tent worm) or beetles (like Japanese beetle) on it this spring or summer? Still, dying that quickly, it almost looks like someone sprayed it with a brush killer. Hopefully you can get a new one at an end of season sale at a local nursery and replace it.