In the movie Adeline meets a man named Ellis, who is quite taken with her and goes to some lengths to win her over. Adeline doesn't want a relationship because she cannot get any older and cannot tell anyone about it, for fear of becoming a laboratory specimen when people, or the wrong people, find out about her condition. In the story though, Ellis woos Adeline and they end up in a sexual relationship. As the relationship progresses, Adeline is more and more cornered by events arising from her peculiar circumstances. She's going to have to tell Ellis or leave him.
One night, after a bout of lovemaking about a month or so into things, Ellis tells Adeline what he feels. He tells her that he loves her. Unknown to him, other factors in the story are threatening to reveal Adeline's secret, and she fears that she cannot tell Ellis. She scribbles him a hasty note, throws her things together and runs away, while Ellis is in the shower. Ellis, not knowing Adeline's secret, presumes that she has run because he told her that he loves her.
Ironically, when Ellis is talking to his father, after discovering her absence, the father tells Ellis that Adeline ran away because "she cannot change." The point is though, that Adeline has changed. The story makes quite clear that Adeline is a product of her era: she meets a man, falls in love, gets married in a church, has a daughter and is widowed when her first husband dies in an accident.
The movie has Ellis and Adeline in bed and having a sexual relationship long before "the problem" of love (or marriage) ever arises between them. It is what the writers, and most likely, almost the entire audience take for granted that is the most interesting thing about the movie. The writer and the director do not seem to realize that the culture has changed out from under Adeline. Adeline, in the modern time, is a "thoroughly modern Millie" who has no problem sleeping with a man she barely knows and hardly trusts and with whom a deep emotional connection is still very much in question. The idea that "this is the way things are" is not questioned at all, by anyone, inside or outside of the movie's framework. What is more interesting is that, for all of the historical change the movie goes to great lengths to portray, the sexual and relationship angle with respect to Western culture and mores, and the changes in the prevailing Occidental philosophies, are never investigated, acknowledged, or portrayed. Have things always been this way throughout the course of history: find someone, start up a sexual relationship with them, then find out if you actually, or possibly can, love one another? No. That has been a sea change in our culture, and very few people even acknowledge it, much less question it.
It doesn't work that way. People tend to arrange their affairs that way, because as sapient, reasoning creatures, we can, but that is not fundamentally how people are, according to nature. In the absence of artificial birth control, sex is much too risky a proposition for human nature to function that way. People have to know that they trust one another, that their partner is a person of character, and that there is an emotional bond and commitment before they get into bed with one another because once they do get into bed, things have progressed too far to mitigate the consequences of a poor choice without large risks to one's survival. Among other things, sex bonds people, even those who have unwisely joined themselves in a sexual union. Biologically, love, character, connection, and commitment are the tests of whether a sexual relationship is advisable, not the other way around, where sex is the test of whether a love match is possible. It is our philosophy and culture that have changed, and the creators of "The Age of Adeline" seem oblivious to this idea. Adeline outlives one cultural norm into the advent of the next without the writers or director so much as acknowledging that this has happened. Interesting.