Dave(hearts)Jade: Dor, Romanian, the longing for someone you love very much, combined with sadness, and implies the need to sing sad songs; its etymology relates it to "dorinta" which means wish
Dave grew up in Houston, he's about as American as they get. He expects he's more American than most, now that most of America is dead (John is practically Canadian, Jade grew up in the Pacific Islands, and Rose is Californian). So he doesn't really have any mourning rituals. Americans sort of don't.
Trolls though, their corpse parties have a sort of class that he only hopes to emulate now. Because Jade is dead, in his arms. His heart aches the way he expects Karkat's did when Gamzee killed Terezi. And he howls, wishing he could turn back time, keep her alive, but that would be pointless. They're doomed anyway.
Saving her life would only doom her to the painful death a doomed timeline gifts its inhabitants. So he crouches by her body and lets the ache in his heart rip out his throat, exploding into the air like an atom bomb. God he wishes she were here, she'd know what to say.
There's nothing left but to sit here with her corpse, give her a proper burial and a proper corpse party, and wait for the dark end that the destruction of their timeline will bring. Time to get started.
He kisses her one last time, knowing that with the destruction of Prospit and LOFAF there isn't any other body for her soul to inhabit, no chance for her to god tier like he did. It doesn't matter; she deserves a last intimate touch. Silently telling her goodbye, in stoic American fashion, he closes her eyes.
"Goodnight Jade Harley." He says, and then there's twelve of him, all in stable time loops (though aside from possible extra dead Dave's there's not too much point to keeping them that way), all busy with some sort of work. Corpse parties aren't all that complicated, but he wants to make it the best. Jade deserves the best.
When he's finished, there's a large funeral pyre (taller than John's house) taking up about a six foot squared diameter. Jade is safely secured on top of it, no danger of her vacating her funeral midway through. He knows he ought to try stuffing her, but he can't bring himself to do that.
So he lights her up, sending her ashes and sparks into the stars, and hums something he thinks sounds like a funeral march (he stops when he realizes it's Star Wars, fuck how could he make such a stupid mistake). But eventually he sits there crying, watching the flames go on and on, as the universe around them crumbles.
"You got a fast car," he sobs, "Maybe together we can – can get somewhere."