Nico never forgave Alex for never coming forward about what he learned of her sister Amy's death and how it pertained to the sacrifices in the Church of Gibborim. Then in "The Broken Circle", one of the last episodes, Gert died during the final battle against Morgan le Fay. I can't shake the nagging feeling that Alex should've been the one to die, redeeming himself in Nico's eyes and earning her forgiveness. Plus, from what we saw, Alex never got the chance to be forgiven by Nico. Obviously, Gert dying was in accordance with her death in the comics, but with Nico's grudge against Alex, I get the sense that either dying in the line of fire or sacrificing oneself to save the others from their common opponent is what it takes to be forgiven and/or for others to perceive someone differently. And knowing that Alex was the one who brought everyone together, the future versions of the Runaways in the final episode, "Cheat the Gallows", could've saved Alex through their actions and convinced their younger selves, especially Nico, not to hold the grudge anymore before they were erased from existence. (Not that I'm complaining, it's just what I think should've happened, anyway).