So in the "Cayde's Stash" mission, you can go into a secret room that Cayde had, and there's some cool dialogue.
He says that the hearts in his deck of cards stood for a girl he loved. When pressed about it, he uncomfortably avoids the question.
Could the girl have been The Stranger? I think either that or maybe Amanda Holliday. But probably The Stranger.
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Ereina-3 or w/e, she's the one he loved and she died. The stranger is a friend of banshee but he doesn't remember.