"Yeah, what are you talking about? I'm not leaving," Xander frowned.
"Yes, you are," Alec said, his voice catching more. "You've been waiting for your chance to leave, to escape, to find your freedom."
"And you think I'd leave you?" Xander demanded, caught off guard.
Alec wrapped his arms around himself. "You already tried once. What else am I supposed to expect?"
Xander frowned. "That was one time, and it was a mistake. You can't... do you still really hold that against me? It was a stupid mistake."
"I know you didn't mean it that time, but you want away! You want freedom from me, for me to stop holding you back, to stop being attached," Alec babbled nonsensically, starting to hyperventilate. He hunched over, panic slowly overtaking him as he tried to convey what he meant, but his words got jumbled. "You have your own friends now, your own life, your own car, you don't need me!"
Shoes and all, Xander walked over to Alec and took him in his arms. Somehow, the pair of them ended up kneeling, and Xander gripped him tightly. "Listen to me," he said hoarsely, "I am never, never, never going to leave you behind. Never! You're my brother. My twin. Mine. I'm not leaving you for anything or anyone. Ever. I'm not going to replace you, and if you don't want Milo to be-"
"No!" Alec yelped, not trying to pull away. "That's not... I like Milo! It's not that."
"Okay," Xander said, "but... is that all?"
"I just... I'm scared to lose you," Alec whimpered, nestling into his brother.
"You won't. I promise. I'll be the safest driver ever, and I'll take you wherever you want to go, and I promise I'm always coming home," Xander assured him.