Is the "scene near the ending" Eirika handing Demon King-possessed Lyon the Sacred Stone of Renais, by any chance? That seems to be the most controversial part of the game.
I like Eirika and L'Arachel's chemistry, but it's a pain that supports take so long to build in this game. I'm grateful for Lyn and Florina's expedited growths in FE7, which allowed me to get them up to C Support in the chapter they joined, B in the next chapter and A by Chapter 18 or so.