I don't know how common this is but I know at least one person who was still really into a guy even after being in a happy relationship for four years and not having seen the guy for a long time.

Never knew what advice to give her.
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RT @thechosenberg
I saw the best minds of my generation destroyed by a Tinder match that went nowhere
https://twitter.com/thechosenberg/status/1653053525008568320