You can always see your listen history within your Recently Listened playlist. When you log in to the Dipsea iOS or Android app, head to the My Library tab, and you’ll find the Recently Listened playlist there, along with your other custom playlists and any series you’ve saved!
Note that any story you listened to will have "Played" and check mark above the story artwork once you have listened to it all the way through. If you’ve only listened partway through, you’ll see a white line around the story title.
Happy listening!