Separation and union are played out on many scales in very minor or very major ways, the third class, second class and the first class Gaudia Vaisnava can experience relatively these feelings and understand something of these matters by studying the books of the Gaudia Vaisnava acaryas.
Sri Caitanya Mahāprabhu has personally taught the six Goswami’s who elaborate fully on the path of devotion from its beginnings to the Param Gatim , the ultimate goal, of Prema Vivarta , meaning a union in separation.
Srila AC Bhaktivedanta Swami has written on these topics, particularly within the Caitanya Caratamrita, and it’s available in every language.
The spiritually of union in separation has its basis of being also eager to be in the association of Radha Krishna, both Srimati Radharani and Krishna Himself demonstrated in their pastimes this union and separation to levels far beyond comprehension as did Sri Caitanya Mahāprabhu. Love means , in spiritual terms , twenty four hours thinking and being in the association of Krishna, Radharani and Their intimate friends and family. If one spends a moment in forgetfulness, one is not really in the spiritual kingdoms.