I am hopeful that humanity will last for a long time to come, but at some point, if the current physicist analysis is correct, then the universe will continue on expanding with all the planets and stars so far apart, and eventually go cold. Devoid of any source of energy, no life will exist no longer, then yes, it is sad. I feel this in solidarity with you.
But my thoughts don't end there because there's reason to be hopeful. This universe is so large that i cannot fathom no other sentient species out there to appreciate life, now or in the future.