Śrīla Sanātana Gosvāmī explains that prema has two sides: meeting and separation. At the time of meeting there is external meeting but something is lost in the heart. One takes the association for granted and the heart is not filled with thoughts about one’s dearest, such as what he is doing and what they used to do together. At the time of separation, however, all the pastimes of Kṛṣṇa fill the heart.
These feelings of separation are transformations of prema, and therefore they can never give pain or unhappiness. Even when Śrīmatī Rādhikā meets with Lord Kṛṣṇa, many varieties of separation moods manifest in Her heart as She experiences madanākhya-mahā-bhāva. Kṛṣṇa was greedy to understand this madanākhya-mahā-bhāva, which contains both separation at the time of meeting and also meeting in separation—to the highest extent—and He thus appeared as Śrī Caitanya Mahāprabhu.
August 27, 2003 Mathurā