Sometimes, when Jean is sure Mikasa isn't looking in his direction, he watches her from the corner of his eye.
She's beautiful and smart; he likes listening to her speak because she's always calculated and intentional. She never makes a fool of herself with ridiculous words and even when she is being irrational, it's rightly so. She's wise and knowledgeable from experiences he's sure she'll never share with him. He's never met someone with as much natural talent as her. These are thoughts and compliments he isn't planning on telling her. They're praises she wouldn't mind hearing, but he's not the person she wants them from. He's someone she cares for, to a limited extent, but he knows he isn't her priority and, in all honesty, will more than likely never be.
He's not stupid. He might be brash and quick to act, and certainly more than a little intrinsically motivated, but these are traits ironically similar to the person she cares about most.
Jean wants to hate Eren.
He wants to, but he can't, despite the feelings he has formed out of jealousy. Eren is the person closest to her and Jean can't help but feel if he weren't around, he would stand a much better chance at winning her over. Jean knows he's selfish; he hopes for a wedge between the pair that he can nicely squeeze himself into.
He comes upon them one afternoon kissing on her bed, Eren's hand on her cheek and hers laced into his hair. Their faces are red even before they realize he's stepped into the room. He suspects this isn't the first time they've done this and can't decide if that makes the situation better or worse. The moment is clearly private, intimate; it fills the room and almost suffocates him. They have the decency to be embarrassed – Mikasa avoiding his eyes altogether and Eren staring straight at him with a redder, more flushed face – but the damage is done.
He attempts a weak, half-hearted promise that he won't tell anyone, flashing a smile as sincere as he can muster. When he leaves, he makes a point to close the door loudly, resting his back against it after he does. He sighs while popping his knuckles and cracking his back.
He laughs, a sardonic sound that echoes around him as runs his hands through his hair. He can hear rustling inside behind the closed door, the sounds of two people scrambling to look presentable.
When he says aloud, "I hate you, you fucker," even he doesn't know which of the two inside his words are directed at.