As we know from the first few episodes this season has multiversal shenanigans. And so far things don’t seem to perfectly align with Season 1. Us being in a different universe would explain that (things like Donald being alive, Mark and Amber still together (Amber being completely different as a whole) or Atom Eve graduating (this could be me misremembering lol, but I swore she dropped out)) They do say only a few universes end up like Season 1 but they didn’t say only one universe ended up like that.
They got back together at the end of the first season after Amber came to visit following Mark and Nolan’s fight.