You're My Best Friend Until You Weren't (Madlyn AU)

Ashlyn has been having a dream about a girl a few days since her junior year started and she can't pinpoint who it was and if it's a dream or a memory.

Or

Maddox and Ashlyn had met when they were kids, but Ashlyn doesn't remember it. So, when Maddox transferred to East High and met Ashlyn after many years, memories began to stir back and so did some feelings.