Depending on what path you are following, (in my case Lexi as my primary, Cara as a backup and some points put into Erynn mostly for friendship purposes and to see more of her story in a platonic way) both Lexi and Erynn randomly at some point say out loud to themselves, they WILL NOT share 'him'. If you haven't seen those scenes, I don't know what to tell you.
As far as the minor cliffhanger ending on the plane, I'd say the safe money is that it's Lakelyn. She mentioned wanting to visit her 'cousin' Lexi, and given mc's reaction of mild surprise and happiness?, it's clearly someone he knows and is on great terms with. If it is her, given her familial connection and obvious bias, I wonder if she ends up being the link to the mc finding his way back to Lexi (assuming she is your L.I., like me).