You're going to die, along with everything that you've ever loved.
Good luck!
Seriously though, you just have to look that shit in the eye and nut up about it. It's going to happen, and there's no sense in worrying about it or crying. If you're lucky, you'll get at least a few more decades on this big ball of mud. And there's zero chance you'll ever actually truly know what's going to happen after that, so it's not going to help to sit and speculate. Whatever you think of as "Yourself" will probably just be gone forever, and it's just a shitty fact of life.
You just have to accept it. Life is a temporary and glorious thing, so take advantage while you can. And sitting around worrying about the fact that it's going to end at some point is ridiculous. What you're doing is the equivalent of losing your erection because you're too busy worrying about the next time you'll get laid while you're having sex.