Swami Vivekananda writes in Karma Yoga: The Yoga of Action,

Every act of love brings happiness; there is no act of love which does not bring peace and blessedness as its reaction. Real existence, real knowledge, and real love are eternally connected with one another, the three in one: where one of them is, the others also must be; they are the three aspects of the One without a second—the Existence—Knowledge—Bliss. When that existence becomes relative, we see it as the world; that knowledge becomes in its turn modified into the knowledge of the things of the world; and that bliss forms the foundation of all true love known to the heart of man. Therefore true love can never react so as to cause pain either to the lover or to the beloved… With love there is no painful reaction; love only brings a reaction of bliss; if it does not, it is not love; it is mistaking something else for love.