They wouldn't believe him, anyway.
They'd say, horrified, "Mr. Shue wouldn't do something like that," and suspicious, "How well do we really know Blaine, anyway?" and whispered, half-laughing, cruel, "Maybe that's why he gets so many solos."
Blaine goes over all the possible reactions in his head, over and over, every time he leaves Mr. Shue's office just desperate to tell someone... and none of those possibilities in his mind ever seem to be in his favor.
He can't tell anyone - but most of all, he can't tell Kurt.
He remembers the way Kurt looked at him when he told him about the Sadie Hawkins dance - remembers the sorrow and horror and sympathy in his eyes - and he hates it, because it makes him feel weak, makes him feel helpless and broken on that cold, cracked sidewalk outside his old school, all over again.
He's not weak, not anymore. He's made himself strong.
So... why can't he stop Mr. Shue?
"No one would believe you over me," Will whispers into his ear, every time, before they're done. "Spoiled... prep school... brat... entitled... little... fag..."
Will comes, taken over the edge by Blaine's humiliation and shame, as Blaine is broken, tears flowing despite himself, burying his red, tear-streaked face in his arms as Will's words echo in his mind, along with other words, familiar words he's heard again and again, if not in an audible voice, in the actions of every male role model he's ever looked to for approval.
"Not good enough... not manly enough. You deserved it... brought it on yourself..."
He knows that's what his dad would say - what he saw in his dad's eyes, the morning after the dance when he woke up in the hospital.
So he doesn't say anything, and he keeps going to Will's office whenever he demands it, and he keeps taking the punishment he's due for simply not being what he's supposed to be.