I keep thinking of Sirius and Regulus blaming each other: Sirius for "choosing the Potters" and Regulus for "choosing their parents over his brother". An endless spiral of pain, crying into the same void of not being chosen, only to realize that they didn't choose each other while expecting to be chosen, again and again simply because.
Sirius was leaving and Regulus was either coming with him or not. Regulus was staying and he was begging Sirius not to leave.
They both feel haplessly abandoned by the one constant they had in each other. There's a gaping maw inside their chests that used to hold the other's soul — they keep feeling at it, mourning and resenting the void of having lost one another. All there is to blame is Sirius for choosing another family. All there is to hate is Regulus for looking at the little dream Sirius had tentatively shown him — them together cast under a light outside their parents' wrath and he still chose to stay.
They meet again in the afterlife and think to themselves how different life would've been if they had just chosen each other.
"I could've plucked up enough courage to ask you, again, if you wanted to come with me. Sought you out at Hogwarts, cornered you somewhere else in the courtyard — anything! I could've asked again. But it hurt so much the first time I felt like you were choosing them over me. I didn't want to risk you choosing them again," Sirius would say.
And Regulus, would give it some time. Let the realization shock him near close enough to bring him back to life, however horrid the prospect of waking up in that dreadful lake truly was...
Then, "I would've. I would've said yes because I'd have known you hadn't left me behind. That I still mattered even when you didn't have to come home and that I —"
"You always mattered, Reg. I could've left way sooner than you all thought but I kept coming back! Each stupid fucking break I'd dread going back but I came home to you. With you, you stupid idiot," Sirius cuts in.
"Merlin, you're such a spoiled little prince still, aren't you? You've never once thought about why I kept coming back even when I hated everyone else!"
"Well you didn't do that great of a job at letting me know I wasn't included when you were raging against the entire family, saying fuck all, shoving all of us under your ceaseless loathing, Sirius!"
"Because you should've known!" Sirius all but shouts. His voice rings in the somber forest of a landscape, unfamiliar to either of them. But calming, at the very least.
"Well I didn't." Regulus says. "And if you had asked again, I would've come with you. Because I really thought you left me behind."
"I never did, Regulus. You did choose to stay too. I wanted to ask again, believe me. But I couldn't anymore. I didn't know you were waiting, least of all for me. I was too hurt and so fucking angry Reg. You think you were the only one feeling abandoned? You broke my heart that night. And you made me walk away without it."
Regulus can't find the strength or bravery to acknowledge the damning fact of his brother's love when put so clearly in front of him to see. The guilt feels like smoke in his lungs. He knows — he knows, he hurt his brother. Very much.
Sirius has a habit of plucking every uncomfortable truth and plopping it down in front of him and Regulus has always been very adept at looking the other way.
Instead, he goes, "Well if I'd have asked you again, if I reached out and told you to come back, would you have gone back? For me?" Not knowing what to expect, or what he himself wants to hear, he asks all the same.
"No," Sirius says. He looks his little brother right in the eyes, making sure Regulus understands his refusal and what he's about to say as well, "But I would've made sure I hadn't lost you. I'd have taken what little you would have given me and ran a mile with it, after the hell that followed me the rest of the break, mind you. I was grieving. And hating you for choosing them. Hating you for staying. I was so angry at you, and James did everything he could to help. I ended up fighting James because I couldn't fight you.
After all of that? And you'd have come to me asking me to come back? I would've taken one look at you, Reggie, and decided that I'd have had you with me before you finished at Hogwarts.
I wouldn't have stopped, not for anyone. Fuck Voldemort. And fuck everyone else and your bigoted ass. I'd have taken you with me."