Heeeeey, finally here. It's your not yet future boyfriend (who is also into technomancy).

Debating maybe something similar to canon, he'll be an old friend and classmate who remembers him? Wei Ying thought he doesn't like him because Lan Wangji is mean and ignoring him.

Somehow they meet again (maybe going to classes together) and just trying to reconnect. Of course, Lan Wangji won't recognize him unless there's a song or a specific event or memory that ties them together.