elves loving men

[Elrian]

I think because of Arwen's choice to love a man she was forced or even mandated by the law of the Valar that she must give up her immortality.

When Elrond made the choice, he was told his children would also have a choice, to sail into the west with him or to remain and become Mortal.
Earendil and Elwing were the first to be given the choice between Eldar or Edain.