For those that have taken the time to read this, thank you.
One of the things that I find frequently about Celica's character in Echoes is that she starts off incredibly strong, but Act 4 is her weakest point, with her decision and her quote before meeting Halcyon (You know which one). While the community has generally accepted Celica's decision about sacrificing herself to Duma to free Mila (P.S Jedah lies, but then again, how was she supposed to know that Mila sealed herself; no one, except Mila, Duma, and, most likely, Rudolf, knew what is up with the blade), the community is still not liking how the game went about Celica's personality in the 4th Act, with her only strong point being in her conversation with Alm. So today, I have taken upon myself to try and figure out what is going on with it.
GhastStation, during one of his playthroughs, has remarked on Celica's decision in the end of Celica's route in Act 4, with it resulting from a lose-lose situation; either Mila doesn't come back, or Celica dies to cure Duma's madness. I generally believe that this is the same situation with Celica's drastic personality change in Act 4. What we know from Celica's character is that she carries the baggage as Princess of Zofia due to Lima IV's behavior, needs to rescue Mila, feels that she should shoulder her responsibilities herself (resulting in her extreme naivety) and is rather lonely, as shown in the game. Oh, and it is mentioned that Celica's most important goal for going on the pilgrimage is so Alm doesn't need to fight anymore and they can live in peace, but that's besides the point.
Actually, that IS the point. The game is somewhat focused on their relationship after all, with it being a first since Blazing Sword with Eliwood and Ninian (admit it. Has anyone noticed that Celica's doesn't turn to Act 4 Celica until AFTER the first battle in the swamp when she meets Jedah, and she doesn't go back to her old self until Alm kills her and Mila brings her back to life? No, just me? Well okay then. When Jedah tells her that the only way to help Duma restore himself is with Celica's soul, Celica realizes that she has two options; sacrifice herself and never see Alm again, or stay with Alm, but Zofia loses Mila and they need to suffer? I don't know about you guys, but them going to Duma Tower kind of makes it obvious which option she took, since Alm laying down his arms (figuratively speaking) is tempting. So when Celica says that cringy quote (while strong on the voice acting, that line was just bad writing; also, you STILL know what I'm talking about), you, the player, could interpret it in a couple of ways, with them connecting to her realization of her not going to see Alm ever again. So when Celica talks to Alm in Act 4, that was more of a good-bye message, since she didn't expect to see Alm in Act 5. Also, she mentions that "I’ve finally remembered why I left the island in the first place." to Alm, which may help this.
And that's it. Feel free to criticize this, add on to it, make memes about it, etc. I know it may not be the this, but I just wanted to share this possibility with everyone else.