This verse is from the Dāmodarāṣṭaka in the Padma Purāṇa. Attachment for Kṛṣṇa in śānta-rasa, rendering service to the Lord in dāsya-rasa, rendering relaxed service in fraternity, and serving in parental love with feelings of maintenance all combine on the platform of conjugal love when the devotee wants to serve the Lord by offering Him his personal body. Thus the qualities of the other rasas combine to form the nectar of conjugal love. On this platform, all the different feelings of a devotee are amalgamated.