The gopis of Brindavan were highly evolved Rishis in their previous births. They longed for the union of God. To satisfy them, during Krishna avatar, Rasalila was enacted. Shri Krishna was hardly seven years old. The Rishis were born as Gopis. By dancing with each Gopi as a separate Krishna, he fulfilled their desires of previous birth. In fact, the Love and longings of Gopis towards Shri Krishna was not a physical affinity. It was the longing for the individual soul to the Supersoul. But, the worldly minded people imagine according to their own views and treat Krishna as One with a body consciousness and criticize him in a vulgar manner. In fact, Jayadeva's Gita Govindam is a depiction that sans any sensuality. But the ordinary people who read those verses imagine those Divine Verses as though they pertain to the ordinary Human beings. It has been clarified this aspect in one of His discourses. Let us not commit the sin of equating of Divine Love with that of ordinary mortals.
Krishna and Rasa leela.
Gopikas (Great female devotees of God) were the sages who were trying to cut the worldly bonds from the past three Yugas. By the end of the third Yuga, they have become all mot successful in their spiritual efforts.
They requested Lord Rama to give final salvation from all the worldly bonds. They were having still the effect of three bonds viz., caste, sex and knowledge. To remove these three effects, they were born as illiterate women in the backward caste as Gopikas by the will of Lord. The six strong worldly bonds (Eshanas) are with body (Deheshana), life (Prashena), life-partner (Dareshana), children (Putreshana), wealth (Dhaneshana) and traditional justice (Dharmeshana). By saluting Lord in naked condition, they have cut the bond with body. After Krishna, they jumped into fire and thus could cut the bond with life. They left their husbands to dance with Krishna and thus could cut the bond with life-partners.