The Myth of Sisyphus by Albert Camus
As for this myth, one sees merely the whole effort of a body straining
to raise the huge stone, to roll it and push it up a slope a hundred
times over; one sees the face screwed up, the cheek tight against the
stone, the shoulder bracing the clay-covered mass, the foot wedging
it, the fresh start with arms outstretched, the wholly human security
of two earth-clotted hands. At the very end of his long effort
measured by skyless space and time without depth, the purpose is
achieved. Then Sisyphus watches the stone rush down in a few moments
toward that lower world whence he will have to push it up again toward
the summit. He goes back down to the plain. It is during that return,
that pause, that Sisyphus interests me. A face that toils so close to
stones is already stone itself! I see that man going back down with a
heavy yet measured step toward the torment of which he will never know
You do not need to justify your hero's failure with metaphysics. You are telling a fable - the myth of Sisyphus, couched in a science fiction setting. Eternal failure, which is torture because somehow it comes with the eternal hope of success.
Mythologic themes are stellar material for high science fiction. Remember for your story - what is the reason that Sisyphus was punished with this particular punishment? I found it interesting that one version has him punished for his levity - with eternal lifting being a suitable punishment!
I see the story - the wedding guest encounters the time traveler after his latest failure. The traveler is intrigued to this time meet the wedding guest, whom he has never met before, and he recounts his tale of failure after failure. But the traveler's eyes sparkle - the levity is still there, and he can see a path forward to success with the next effort. That is his fate.