Connection between Guru and disciple is for many births

(from "Autobiography of an Avadhoota - part 2"):

Avadhoota Nadananda: Cruel time plays tricks in human life now and then, when one tries to make a permanent connection on worldly terms. It is only the relationship based upon spiritual purpose and pursuit that continues through births. Such a relationship between Guru and disciple is not created for the worldly benefit and continues to exist forever, however weak, fruitless, and tasteless it might seem sometimes.

No other relationship however good - be it wife, husband, mother, father, or son that may happen to get in any birth, will continue with us in the following births. But the connection with the Guru however bad it might seem at the time will definitely continue and we will always be in contact with him. This is the wonderful arrangement of the Almighty for the protection of his most loved creation called the human. This is because God is human-like, and not because humans are god-like. But his own replica called a human does not have time to feel the intensity of this love that the Lord has in his bosom for us. At the very moment one recognizes this pure devotion for him in our heart, it will pour out in gratitude.

(from "Living with My Himalayan Master: Sri Sri Bhajan Brahmachari"):

Thakur [Sri Bhajan Brahmachari] would often say that he went to each place because there were souls connected to him from other births who were waiting, who needed him to bring them back to the path of spiritual sadhana. Once he told me that the Guru comes again and again to take the disciple through the next stages of soul evolution. The journey started with the Guru continues birth after birth, until one if free from the cycles of births and deaths. The disciple cannot see the past lives of the Guru, but the Guru, if highly enlightened, can identify his disciple birth after birth. The guru-disciple relationship as a continual journey together. He also told me that the Guru is not totally free until all his disciples attain mukti or moksha.

The true teacher is one who has transcended the egoic mind to the realm of egoless universal self. The seed of compassion remains with these masters while the past and future are burned in the fire of self-illumination. That is the reason the Guru needs to have the responsibility of walking the disciple through the haze of egoic mind to the light of eternal Truth. It is a divine destiny that each exalted Master who is like living Buddha promises to come again and again to earth to guild the disciples to the ultimate state of self-realization. This is the supreme state of selflessness and divine love.