[Anguirel]

I'm with Lush on Beren and Luthien. I found the "slain by bliss and grief" passage rather more than you'd expect even from embracing the most beautiful thing in existence. Also it explains Luthien's later tenacity when Beren continually sets off without her. They are married already, in Elven terms.

Aragorn and Arwen, on the other hand...it could easily have happened in Lothlorien, when that mischievious match-maker Galadriel dolled Aragorn up. But in Aragorn's case, I doubt it somehow. Beren was under no promise to Thingol when he first met Luthien, and after his vow they always considered the option of running away and living in the wilderness together, as befits husband and wife. But Aragorn wouldn't break his promise to Elrond, or force Arwen to mortality prematurely; he'd wait till he was King of Gondor and Arnor.