I think when you live so long, as in possibly forever, that after a while all life will be at best bittersweet. The best part being is that all will come to the halls of the "dead" (I know that isn't it, and someone will correct me). After so long and losing all that you built and was important to you, you just give it up, so to speak. Think about it when you wish that you could live forever. Hence, the "gift" to men of death.
One reason I'd rather not be an Elf. As an aside, if all or most of the Elf stories end tragically or bittersweet, why are some of the Rivendell Elves "merry as children"?
. I think that this is probably the "hook" that the Ring used to reel Boromir in.
LOL. I get this mental picture of Boromir with a fishing line coming out of his mouth! But indeed the Ring has him hooked now and I think Boromir is fighting the Ring as much as Frodo is from now on.