CRAIG BOWKER JR.: Whoa! A Potter? In Slytherin? (1.4.29)
Albus feels like he has betrayed his family name by being sorted into Slytherin. Or does Albus actually want to betray the family name, like many fifteen-year-olds before him?
ALBUS: At Harry Potter and his disappointing son. […] At Harry Potter and his Slytherin son. (1.4.59, 1.4.61)
Harry grapples with guilt about people dying because of him. Albus grapples with the guilt of betraying his father. So he wants to fix that by undoing what makes his dad guilty, and by doing so he betrays basically everything. It's a vicious cycle.
ALBUS: I just wish you weren't my dad.
HARRY (seeing red): Well, there are times I wish you weren't my son. (1.7.42-1.7.43)
This is a brutal exchange, and their relationship as father/son will be forever damaged. But neither one is lying. Is it possible to betray someone with the truth?
HARRY: I need you to stay away from Scorpius Malfoy. (2.8.53)
Harry continues to betray his son's trust by forbidding him from seeing his only friend. Will Albus ever be able to trust his father again?
GINNY: Harry, you have one of the greatest hearts of any wizard who ever lived, and I do not believe your heart told you to do this. (2.13.5)
It's the alternate-timeline Harry who bans Scorpius from Albus's life. This is the timeline where Ron and Hermione didn't marry. Is Harry different in this timeline, or is he the same as usual?
SCORPIUS: How did Cedric become a Death Eater? What have I missed? Find me some—light in the darkness. (3.4.2)
Scorpius and Albus think they're saving the day by keeping Cedric alive, but Cedric betrays them by turning to the Dark side.
SCORPIUS: Are you still undercover now? Are you still secretly working for Dumbledore? (3.5.10)
Betrayal isn't always considered a bad thing in the Harry Potter universe. Snape is held up as a hero for betraying Voldemort and turning to the good side.
YOUNG HARRY exists, disturbed, as ALBUS bursts from within VOLDEMORT's cloak. He reaches out a desperate hand towards his dad. (3.13.19)
Harry's dreams are a mess. It's like he can't figure out if his own son might turn against him and betray him, or if Harry will betray his own son. (We think it's both.)
DELPHI: I don't just want you to stop him. I want you to humiliate him. (3.19.11)
Delphi betrays Albus' trust by turning against him and using him as a pawn to revive her dead father Voldemort. With her, betrayal leads to more betrayal, as she wants Albus to ruin Cedric's reputation, again leading to the bizarro Harry's dead world.
HARRY: The Boy Who Lived. How many people have to die for the Boy Who Lived? (4.6.18)
Harry feels like he betrays many people simply by existing, and he carries a lot of guilt because of this.