Humans always have some existential disaster looming, be that plagues, famine, wars, natural disasters etc. It's a feature not a bug, you need to get used to it and stop catastrophising. Who knows what the future holds? Not you or I that's for sure.

Even if the worst happens, it will pass and we'll survive. Those who are left will pick up the pieces and carry on, just like always. People die all the time, what's the surprise there? You're going to die, maybe sooner, maybe later, but it will happen. Seems like you're having trouble accepting death. Pain, separation, death, these are all features not bugs, you need to find a way to accept it because these things are never going away in this mortal realm. Cherish each moment and live with joy and love.