He sees the way Benny's eyes change, the look on his face, the way he can't look away, and he can't allow himself to think about that, what it means - except that he can't stop the awareness of it or the way it makes his breath catch.
There's blood on his neck and Benny's just stood there, in control enough to stop himself from doing anything but evidently not enough to let himself look away.
Dean breathes deep, doesn't look away either. He asks "you okay?" only when he's pretty sure his voice'll be steady enough to pass for normal.
When Benny says "'M fine," it doesn't sound like he means it and Dean thinks that there's anger in his face as well as intent, like he hates whatever it is that the blood on Dean's neck is making him feel.
And it shouldn't hurt when Benny turns away, starts walking, but it does - same way it always does when someone leaves him feeling like he isn't worth their time - and, fuck, if Dean doesn't know that that's not what this is; if he ain't sure this is about Benny and his whole lifestyle more than it is about Dean and whatever fucking issues he's got going on - but it hurts all the same. And Dean wants to think, all noble and self-sacrificing, that letting Benny drink from him would've been something he could have done to help him, that if he'd just volunteered himself, it would have been for Benny's benefit. Only he knows that isn't true at all - knows it would've hurt Benny, more than likely, been the kind of temptation he shouldn't offer to someone who's resolved never to feed on a live human again. For Benny, it probably would've been a cruelty, more than a kindness, to offer him the one thing he couldn't and shouldn't have. It would have been selfish to ask Benny to lean in close, just because he wanted it, to have him lick the blood from Dean's neck, suck at the wound and dig his teeth in just a little, make Dean's breath do more than hitch a little.
But, if Dean's honest with himself, that was what he wanted, for all that it'd do neither of them any good. And he tries not to say it, tries to send Benny on his way, make a clean break, and not ask anything of him - since he's already ruined this, this homecoming, because his damn brother wouldn't leave Benny the hell alone.
So, Dean tells himself he's never going to ask, never going to let Benny see him bleed, make Benny want it the way he does (remind him of the way he seemed to want it, too), because Dean knows it can't end well for either of them, if he does.
Sometimes, though, Dean lets his hand linger on his own neck, can't keep himself from imagining how it might feel; and sometimes he catches Benny looking. Benny won't even kiss his neck, Dean notices, as if it's too much of an enticement, too close to what he really wants. And Dean wants to feign ignorance and ask him to, or use a hand to guide Benny's head there, so he can feel the way he'd fit, feel rasp of Benny's beard, feel his mouth trailing over skin.
He thinks Benny would keep his lips pressed closed, if he did agree to it at all; but he knows he'd imagine the teeth anyway, just grazing the skin. And he's afraid he wouldn't be able to stop then, keep back that one last request that might leave neither of them able to stop at all. And Dean knows there are some things he doesn't have a right to ask.