I don't even know who to root for anymore. We, the readers, are getting tossed in a lot of directions and none of them are particularly compelling. But for the sake of getting my thoughts out, this is what I have in mind:
A) Lemon confesses that she lied in the past and her and the MC sort out their problems or
2) Other main girl who's not Lemon who's name I totally remember makes a move, Lemon's and MC's past comes out and she either: 2a) reacts really positively and helps them through it or 2b) reacts negatively and this is just another hack manga or
III) the best friend takes both girls for himself and the story ends before the train can wreck itself