ALBUS: So we need to choose now who to be friends with for life? That's quite scary. (1.3.7)
The idea that Albus needs to choose his friends for life is ridiculous, but in context, it makes sense. His own father, and Rose's parents, all found their BFFLs on the first day on the Hogwarts Express.
HARRY: Maybe if you tried making a few more friends… without Hermione and Ron I wouldn't have survived Hogwarts, I wouldn't have survived at all.
ALBUS: But I don't need a Ron and Hermione. I've—I've got a friend, Scorpius, and I know you don't like him but he's all I need. (1.4.68 – 1.4.69)
Is Harry being truthful here? Does he want Albus to have "more" friends, or just "friends who aren't Scorpius Malfoy"? Whatever his intentions, is he right? Should Albus try and make more friends?
SCORPIUS: Come to the funeral. […] And be my good friend. (1.4.129-1.4.131)
Albus and Scorpius don't simply become friends because Scorpius shares his candy. They become friends because they're there for each other in times of need.
SCORPIUS: You're better [than Harry Potter]. You're my best friend, Albus. (2.6.13)
Scorpius knows how to give a well-timed, genuine compliment…which is more than we can say about Harry.
DELPHI: You're best friends. Every owl he sends I can feel your absence. He's destroyed by it. (2.14.19)
Delphi may be evil (or close to it), but she is kind to Scorpius here, letting him know that Albus is his good friend. Why does she do this? Wouldn't Albus be easier to manipulate if he were alone? Does she have an ulterior motive?
DELPHI: You know, I didn't have a best friend when I was your age. (2.14.23)
And that's why Delphi is evil: she's alone.
DRACO: I always envied them, you know—Weasley and Granger. I had—
GINNY: Crabbe and Goyle.
DRACO: Two lunks who wouldn't know one end of a broomstick from another. (2.15.8)
Draco proves the point that having two friends doesn't matter if your two friends are callous idiots. It's the quality of friends that matters, not the quantity.
SCORPIUS: You have no idea how good it is to see you again. (3.9.100)
Most of Act III is about Scorpius risking his life to change time in order to bring Albus back. That's an intense friendship.
HARRY: No, she doesn't deserve that. You have a right to be angry. You all do. But this is not all Hermione's fault. (4.1.17)
Well, it is all Hermione's fault that the kids found the Time-Turner, but Hermione stood up for a lot of stupid things Harry did. It's only right that he return the favor.
HERMIONE: He'll hug you. Because we're all on the same team, aren't we, Ron? (4.7.16)
Yes, you read that right. Draco Malfoy has finally been accepted as part of the team.