Call Back: To the episodes "Goes Cellular", "All Dried Up", "Wet All Over" and "The Busasaurus".
Captain Obvious: After literally bumping into Arnold's parents while trying to sneak out of his bedroom at 2am, Phoebe says to the girls that she's hugely ashamed because now Mr and Mrs Perlstein will think that she is "the tramp who seduced their son." Wanda points out that Phoebe is the tramp that seduced their son.
Faux Yay: The girls (D.A. included) all make jokes about D.A. being a "little lezzie" who is in love with Phoebe. She even pretends to hit on Phoebe to cheer her up. When D.A. is moving to New York for college, she says goodbye to her friends before boarding the plane:
Phoebe pulled her into a tight hug, and both girls sobbed. Carlos went over to them and said, "Pheebs, if you wanna give her a full on kiss-with-tongues good-bye, I have absolutely no problem with that."
Foreshadowing: Early on, Arnold tells Phoebe that she deserves to marry "some rich Southern gent". When they meet after three years apart, she's dating one.
Framing Device: In the prologue Phoebe, having just finished college, picks up her copy of the Fantasmic Four's scrapbook and begins to read. In the epilogue, she puts it down and it's revealed that she and Arnold are back together and she's pregnant.
Freud Was Right: Invoked in-universe. On prom night (in a Call Back to "Goes Cellular") Wanda decides that the post break-up tension between Phoebe and Arnold was caused by them not having "break-up sex", failing to grasp the subtleties of two people splitting up for no real reason when they're still in love with each other. Turns out she has a point...
Heroic BSOD: Arnold has a minor one after Phoebe dumps him.
High School Dance: Occurs about halfway through the story and is the plot's first major climax.
Hilarious in Hindsight: Invoked by Wanda at the end, describing the following: when D.A. is leaving for New York, she tells Phoebe she will find someone better than Arnold. Not only does D.A. invite Arnold to her wedding, but he gets back together with Phoebe there.
Only Sane Man: At one point, Phoebe becomes upset when Arnold sends Ralphie and Carlos to return a photograph of Arnold and Phoebe in fourth grade that he slept with under his pillow during their relationship. It seems that he means this as a sign that he has accepted her insistence that they get over each other (although he tells her he will love her forever), but it breaks her heart again and she seeks comfort from D.A. The latter sees Arnold's actions as shabby, manipulative and cowardly, and such treatment of Phoebe pushes her Berserk Button. Her first reaction is to yell at Carlos about it, and then announces she's going to talk to Arnold, telling her boyfriend to wait where he is for her. She goes completely mad at Arnold, leaving Keesha (who can see both sides of the argument) as the Only Sane Man (Wanda is exempt because, as she would cheerfully admit, she was born holding the Idiot Ball).
D.A. also has a moment of this, when Phoebe asks the girls if breaking up with Arnold is the right thing to do:
"You're doing the realistic thing," D.A. said. "Doesn't mean it's right."
Phoebe: (to Wanda) "Apparently, I slept with Arnold."
Your Cheating Heart: The guys all remain friends after they go off to different colleges. So do the girls. Carlos and D.A. and Keesha and Ralphie remain in their relationships. Three years after Phoebe leaves for North Carolina, D.A. and Carlos get married. Wanda, Keesha and Phoebe are their bridesmaids. The whole gang are reunited at the wedding, and Phoebe and Arnold end up in bed despite both being in relationships with other people. They get married three months later.