That's the real problem of loving them: they just don't live as long as we do and we must be prepared to say goodbye to them all too soon. I wish there was something we could say or do to ease the pain of loss, but there really isn't, other than to acknowledge that we all go through it if we give our love to each other without holding back. They give us so much, but saying goodbye is never easy.
Emily Dickinson expressed it in this poem:
My life closed twice before its close;I send my blessings out to all who grieve, including myself.
It yet remains to see
If Immortality unveil
A third event to me,
So huge, so hopeless to conceive,
As these that twice befell.
Parting is all we know of heaven,
And all we need of hell.