The story
From back (adverb or noun) + friend. Sense 3 (“person who pretends to be someone’s friend”) may allude to a person who stays back instead of coming forward to help, and so is not a true friend.
Etymology from Wiktionary, CC BY-SA 4.0.
backfriend
back·friendToday it means: A friend who supports someone; a person who has someone's back; a backer, a supporter. Full definition →