Because there is no verifiable evidence to prove there is an afterlife, many Humanists either disbelieve or are agnostic on the subject. Most Humanists find ways of dealing with the thought of their own death without causing problems enjoying their life.
One age old notion is to ask what was your life like before you existed, and point out that if there is no afterlife, then non-existence after death will be no different than non-existence before life. And because there is nothing you can do to prevent eventually dying, this one life we know for sure we get to live takes on increased importance, especially in regard to taking the actions we can to live a long, happy, healthy, helpful life.
Another idea is to consider how our bodies are made up of the same basic materials that have been created by the stars for billions of years. And after we die, those same star materials will continue on in different forms as part of a continuing natural world.
Another is to think about how our actions and existence has affected people or things in the world, and to feel satisfaction that our influence will continue on for several generations or even longer.
Another is consider the amazing reality that we are one tiny part of our universe that became conscious of itself to the point that we could consider our own place in existence. This is by all accounts something to be immensely privileged and grateful for even if it will come to an end.
And for anyone that doesn’t find these views at all comforting, you can always take solace in the fact that, while there may be no verifiable evidence to prove there is an afterlife, there is currently no way to disprove the possibility, especially if it involves something we might label as either supernatural or at least beyond our current understanding.