Hope Is A Killer
He holds Harry back. Only Harry prevents him from diving through the archway after Sirius. He says the words, and he can hear his heart breaking in his voice. But Harry won't listen, won't believe.
He doesn't want to believe it either, but he can't hope. Hope is a killer. He knows that all too well. It lifts you up and grinds you down, over and over again. This is what his life has taught him. He's had the hope beaten out of him after all these years, all the disappointments. He refuses to indulge in it again.
Instead, he focuses on reality. On what he knows will happen next.
After ensuring Harry is safe with Dumbledore, he will go back to Number 12 Grimmauld Place and he will get stinking drunk.
Tonks will find him sometime after midnight. She'll have been drinking as well, will be crying and hiccoughing, looking very young and lost. He will catch a glimpse of his own reflection and see the evidence that he's old before his time.
He won't even have to ask. She loved him too, in her own way. She'll offer with a silent look and the quick darkening of her hair from pink to black. A slight change and her features will become horribly, achingly familiar. They will lean into each other for a kiss.
But she will taste -- smell -- feel wrong, and he won't be able to maintain the charade. She will cry harder as he throws the half-empty bottle of whiskey against the wall to shatter and stain the carpet. Libations for the dead, he will think, as they try to comfort each other and fail. She will leave him in reproachful silence.
He will wake with a hangover and a sharp ache in the small of his back from sleeping hunched over in a chair. It will take him a moment to remember. He will be looking for more whiskey when Snape arrives and sneers at him. They will almost come to blows, the last of his famous restraint gone in the face of this final loss. Why bother with the niceties? Snape won't expect them from him, and it will take all the energy he can muster not to break down. He will have nothing left to indulge the man's schoolboy grudges.
He will walk away, wondering how Voldemort can fear death so much when death is the only thing he longs for. The hunger for it will burn in his belly, rise like bile in his throat to settle, sour, on his tongue. It will prickle just beneath his skin, pulse through his veins. They will feel it pouring off him in waves and they will not leave him be. They will fear what he may do in the wake of this loss and they won't even know he has a knife, he has poison, he has a gun he picked up in his travels across the world. Those who knew him the first time around will brace for the continuous drinking and the reckless behavior, the complete lack of care he will take with his own life.
But he's older now, and will not indulge in that foolishness again. There is too much riding on his shoulders; he is Harry's last link to James and he has to fulfill Sirius's promise. He will not take his life today, nor the day after. He will simply excise hope from his heart, and carry on in his despair.
He sees all of this and more stretching before him in the moments after Sirius falls, as Harry struggles in his arms. Although he's never been gifted with the Sight, he knows he has Seen truly.