A term one would use if they were missing a past relationship.
It originates from the Macroscope song WYZ, as it is written by the frontman of the band about him missing a one of his previous girlfriends. WYZ as a title means "Missing The X", which can also be read as "missing the ex", the meaning of the song.
Boy1: ‘God i miss my girlfriend’
Boy2: ‘Dont worry about it, you’re getting WYZ Vibes’
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