Vereesa Windrunner has lost everything several times now.
She lost her oldest sister Alleria to the same Horde invasion that killed most of their family, as Alleria went off to seek vengeance against the orcs and ended up lost somewhere beyond the Dark Portal, never to be seen or heard from again. Her other sister, Sylvanas, was killed by the Lich King's servant Arthas Menethil, and the death knight chose to prevent Sylvanas from even attaining the peace of death, trapping her in undeath.
Worse, when Vereesa lost Sylvanas, she lost her homeland and her people. The high elves of Quel'thalas became blood elves, following Prince Kael'thas on the path to ruin, addiction, and madness and she could not, did not follow. Along with a few remnants of her people, she attempted to preserve what had been thrown away, to keep high elven culture alive even as Silvermoon resided in the hands of those that had abandoned it. Its not surprising that she found love in someone who shared her loyalty to the Alliance, nor perhaps is it surprising that she found it in human arms, as both Alleria and Sylvanas showed a predisposition to humans.