---Alec's POV—
He'd cared for Jace so deeply and for so long that he had never even considered the possibility of finding happiness with someone else. For Alec, there was never really a moment of "discovering" or "realizing" he was interested in men. There was only Jace. Always Jace. He knew it was wrong, looked down upon, but it wasn't until years later he realized his feelings for Jace indicated a preference for men. Still, it didn't matter. Only Jace mattered.
But even as a child, just coming to terms with the depth of his feelings towards his parabati, he knew that it could never be.
Because the feelings weren't returned.
Because he was a shadowhunter- a warrior.
Because the Clave would disapprove, his parents would disapprove.
Because he wasn't brave enough, strong enough, he wasn't good enough for Jace Wayland.
Even if Jace did have a preference for men in fighting gear, Alec wouldn't have a chance. Jace would never be interested in someone so plain, someone so weak. No one would.
So this was his secret. His exception to his long-held belief in Truth Above All Else. He decided a long time ago to keep his interest in guys in general and Jace in particular to himself.
He was better off keeping these feelings bottled up and letting them gnaw at him every time he watched Jace's eyes light up when he spotted Clary's small frame in the distance. He was better off letting it all fester as he watched Isabelle flit from one boy to the next, irrespective of species, without having to worry about the Clave passing judgment on her love life. He was better off letting it kill him inside every time he witnessed a rare moment of intimacy pass between his parents- a shared glance, a private touch, knowing he could never have that with anyone, no matter how much he craved it.
Alec made his decision. He was going to follow the same mantra with his feelings that he followed when fighting demons: It's always best to err on the side of caution.