I don''t understand the monologue at the end. Who is talking, and who is "you"?

Speranza is talking and she meant it in a general sense (like you live in this world and you die in it), she's probably the last living human in the world, yet had no purpose staying in the facility all her life.

I wonder if Mama will actually be okay, Liberta probably just came up with that in the heat of the moment excuse to get Speranza to leave... it actually made me tear up

if they had that mask the whole time couldn't she just come and go as she pleased?

Maybe they only had enough filters for one trip? There is also an implication that Mama did not want Speranza to leave, so she simply never told her that this was an option.

im ngl, i think she'll die before they reach the research center and come back. and i think mama understands very well that the mask is not enough to be anything other than a last resort. given that all three of them might as well be on death's door, itd be time to go out and enjoy the world in the end