To hear America tell it, Aspen is so good-looking that he makes Brad Pitt look like a troll and so compassionate that he makes Mother Theresa look like a Satanist. America's not entirely wrong—Aspen is indeed a kind, caring, and hunky dude—but this one of the many instances when America is blinded by her love for Aspen.
That being said, there's no disputing that Aspen is a pretty great dude, especially where his family is concerned. That doesn't life is easy for him, though. It'd be hard enough if Aspen and his family were just Sixes, but Aspen's dad died three years ago, which means that this eighteen-year-old is now his family's main provider.
This forces Aspen to make a lot of sacrifices: he often gives "his share of the little food they had down to his siblings" and mother, even after an exhausting day of work (2.31). That's selfless. America loves Aspen for this dedication, but she's sometimes concerned about him overworking himself. As she says, "Aspen, I know you could do it. But you're not a superhero. You can't expect to be able to provide everything for everyone you love" (2.42).
Here's the thing, though: America is only sixteen years old. Although her feelings for Aspen are very real, she and Aspen are both so young that there's no telling how things will end up between them. This uncertainty is amplified by the fact that Aspen is from a lower caste than America. Simply put, marrying him will give her a much lower quality of life. That's just how it goes.
America might not fully grasp this, but Aspen sure does: "I can't make you like me. I can't stand the thought of you hungry or cold or scared. I can't make you a Six." (5.40)
That's some real talk, Shmoopers.
This uncertainty leads Aspen to convince America to enter the Selection, but even he doesn't expect her actually to be chosen. In true teenage fashion, what follows is a big blowout fight that seemingly ends their relationship. And we all know what happens next: America falls for Prince Maxon, but Aspen suddenly appears as a palace guard after signing up for the draft. Needless to say, it takes the pair roughly one day to start making out like fiends once again.
There's just one issue with all of this, however—America is a changed woman. It's not just that she has feelings for Maxon. It's not that she loves Aspen any less. It's not even that she doesn't want to be a Six anymore. It's that she's grown as a woman over the course of the Selection, and this maturity has made her realize that she needs to focus on herself before she can choose between Maxon and Aspen. And if our boy Aspen is half as amazing as America says he is, he'll accept her decision and be right there waiting when she's ready.