As soon as love is truly awakened, the moment of time is transformed for it into a form of eternity. Even erotic egoism cannot forbear swearing “eternal fidelity” and, for a fleeting moment, finding pleasure in actually believing in this eternity. How much more, then, does true love want to outlast time and, for this purpose, to rid itself of its most dangerous enemy, its own freedom of choice. Hence every true love has the inner form of a vow: It binds itself to the beloved and does so out of motives and in the spirit of love. Love for a time, love expecting a time of break-off, is never true love.
–Hans Urs von Balthasar, The Christian State of Life–haven’t read; found quote here