This was another story idea I got as a dream.  I suppose it reflects my mood lately with everyone seeming to get older around me, not just physically but mentally as well.
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Two friends have known each other all their lives.  They are able to time travel but only by skipping forward in time.  They've been doing that for a while and have experienced centuries of history past by, but one day, one of the friends loses this ability.  The other is torn between staying with the friend or leaving the friend behind to continue skipping forward.  There was a sense before that both of them were destined to see all the Earth's history to the very end until the world goes dark, but now that seems less certain.  They end up splitting ways, with one living through the years instead of skipping forward while the other continues to jump forward every few years.  Each time they catch up, one friend gets much older while the other remains youthful, causing a lot of despair as the younger one now literally watches the other waste away through time with everything else.