Long years have passed. You did not have the cares you carry now. Do you remember what I told you?
You said you'd bind yourself to me, forsaking the immortal life of your people.
And to that I hold. I would rather share one lifetime with you than face all the ages of this world alone. [Arwen hands Aragorn the Evenstar]
I choose a mortal life.
You cannot give me this.
It is mine to give to whom I will. Like my heart".
I love this dialogue between Arwen and Aragon. It is utterly beautiful and clearly demonstrates the steadfast yet magical love they share.
Though romantic love may be seen as the most transient, it's fragility stemming from the conditions applied to it. It can also be the most amazing because it is something actively chosen by the heart.