"She had been about to say that this was like an adventure, like a brave experiment, but in just the past few hours Henry had stopped being a boy who might have believed that. He was now a boy who climbed without comment into the backseat of a rental car, which was full of their belongings, inelegantly packed, and lit out for some unexpected territory. He was a fugitive from other people's eyes. They both were, actually. (16.282)
Some kids enter adulthood when they find out the truth about Santa Claus (he doesn't eat everyone's cookies) or when they're allowed to babysit for the first time. Unfortunately for Henry, his childhood ends when he watches the other parents in his school shun his mother because they all know his dad murdered another Rearden parent with whom he also happened to be having an affair. And we thought our preteen years were tough.
[What] did any of it have to do with her now, here, huddled beneath a brand-new duvet in her parents' bed with her twelve-year-old son, for how long? Until the end of the night? Or the news cycle? Or the year? Until the nuclear winter ended and somebody (who?) gave the all-clear. (17.286)
Realizing that nobody else is going to make your decisions for you is a big part of growing up, and even though Grace is a fully-grown woman, she's never really had to come to terms with this fact before since she went straight from her childhood home to college to marriage.
Now, inhaling and then watching the white smoke rise, she felt as if some great Pause button had been depressed when Jonathan stepped into her life, and only this instant had the finger come away and released her forward motion, and suddenly she was back at precisely that earlier moment, a college student again, with most of the big decisions and the big events still before her. Though this time she had been issued with a child and a nominal profession. And a book about to be published. Or so it had been when she'd left the city. (17.291-292)
Somebody call Rachel Platten; this is Grace's "Fight Song" moment. She's already recognized that Jonathan immediately became the most important person in her life the moment she met him. Now that he's gone, she has a chance to reconnect with her pre-Jonathan self and move forward.
"I want him to sleep on my bed," Henry said from the backseat. "And if he goes, I'll clean it up. He's my dog. I'm responsible." (22.392)
Henry is really stepping up to the plate and proving he can be trusted to take care of another living being—which is more than Jonathan's family could say for him.
This was the moment it finally broke through to her. That apartment, that home, was gone. Like her marriage. Like her husband, who was now thousands of miles away in a cold place, asking for her forgiveness. (23.423)
Grace's attachment to her childhood apartment (a.k.a. her current NYC apartment) is like no other. By this point, she knows every terrible thing Jonathan's done and every lie he told her. Still, it's not until she realizes that she can't go back to her apartment that she accepts her marriage is over.
Now she was a sturdy baby with a halo of thin brown hair and a pair of bottomless dimples, muscular little legs, and an enthusiastic interest in Grace's ear. She was also a once and always child of tragedy, whose father had killed her mother, whose other father had rejected her, and whose brother had disappeared from her life, forever. And she was only six months old. She still, Grace saw, had the long, beautiful eyelashes she remembered from the time they'd met before. Like Henry's eyelashes: also beautiful, also long. (21.387-88)
Obviously, Abigail Elena has done most of the growing in this particular quote, but it shows how Grace has grown too. To be able to look at her murderous ex-husband's love child, notice their similarities, point out her similarities to Henry, and not completely spiral into depression is more than we would have expected from Grace—or really anyone in that situation—a few chapters ago.
It had been exactly as terrible as she feared. But at least it had not been more terrible. (22.401)
It, in this case, is "reading the articles about her husband's crime and the associated judgmental comments." Grace avoided any and all news from NYC like the plague when she arrived in Connecticut, so finding the strength to take it all in is a big step forward in her personal growth.
Grace waited at the half-opened door until he was gone, but she didn't go back inside right away. Instead she stood there, listening for the utterly familiar sequence of groans and clicks as the elevator made its descent, until at last she heard the far below scrape of the gate, releasing him into the lobby, and the rainy and dark midafternoon, and the street where she used to live. (24.438)
This moment is the final sentence in the book, and while listening to an old elevator might seem like one of the most anticlimactic endings in literature, it's very meaningful for Grace. She's heard that elevator going up and down for almost her entire life, and she's finally packing up to leave for good. That's enough to make anyone a little emotional.
Was it possible that he was actually...really...okay? (22.392)
Grace mentions how much Henry has changed and grown physically several times throughout the book, but here she's reflecting on his emotional and mental state. He doesn't seem like a broken, damaged kid who sits in the back row listening to BTS. We think she's overestimating how "okay" he is, but we agree he's not falling apart.