Perfection of pure devotional service is attained when all attention is diverted towards the transcendental loving service of the Lord. To cut off the tie of all other affections does not mean complete negation of the finer elements, like affection for someone else. This is not possible. A living being, whoever he may be, must have this feeling of affection for others because this is a symptom of life. The symptoms of life, such as desire, anger, hankerings, feelings of attraction, etc., cannot be annihilated. Only the objective has to be changed. Desire cannot be negated, but in devotional service the desire is changed only for the service of the Lord in place of desire for sense gratification.
HDG A.C. Bhaktivedanta Swami Prabhupada 1.8.42
Affection and love develop
Just like love between two persons, it cannot be forced. "You must love him. You must love her." Oh, that is no love. That is not love. When automatically you love one another, that is quality. Dora vede(?) prema…. But gradually, remaining together, the quality of love increases. Then the wife takes care of the husband, and the husband takes care. They become bound up, united in love. That is quality. Morning Walk -- November 2, 1975, Nairobi:
The affection that maintains devotees
Actually, in this verse the word rajaḥ means not “passion” but “affection.” In the material world, rajo-guna is passion, but in the spiritual world it is affection. In the material world, affection is contaminated by rajo-guna and tamo-guna, but in the śuddha-sattva the affection that maintains the devotees is transcendental. /sb/10/13/50
Six Signs of Love
"The whole system was that. Love exchange. I give you some service; you give me something, out of your love. Dadāti pratigṛhṇāti. Love means six symptoms. I give you something; you give me something. I give you something for eating; you also give me something for eating. Dadāti pratigṛhṇāti bhuṅkte bhojayate, guhyam ākhyāti pṛcchati (Upadeśāmṛta 4). If I am in trouble, I express my mind, I open my mind before you, and you also try to help me. These are the six signs of love. That is Vedic civilization—everything exchange of love. No business, mercantile."
(Srila Prabhupada Lecture, Los Angeles, June 22, 1972)