Lyric discussion by bassisbetter 

Cover art for Harvest lyrics by Neil Young

To me, it seems like it's about a man who's girlfriend's mom is dieing, and he's giving her a promise that even when she's gone, she'll still have him. Since she's losing her mother, she feels sddenly lonely, and tries to fill the void with others (did I see you down in a young girl's town) And the "did she wake you up to tell you that it was only a change in plan" would be her receiving the news about her mother dieing. And him saying "dream up, let me fill your cup with the promise of a man" is him saying that you should never feel lonely because he's there.