Radharani and Krishna has been discussed as mundane lovers , which is not appropriate. Love and marriage are too small words to define such sublime relationships.
Rukmani is the one, whom Krishna married. Rukmani is incarnation of Goddess Laxmi. whereas Radharani is the original source , from which Goddess Laxmi has emanated.
Rukmani Devi is a perfect example of devotional aspect of Krishna. She never saw Krishna, but just be hearing Krishna’s stories and pastimes, she fell in love with Krishna. Without even meeting or seeing Krishna, she decided to marry him . She knew about Krishna’s pastimes at Vrindavan. She knew everything about Radharani and other gopis.
In the Vaishnava devotional or bhakti traditions of Hinduism that focus on Krishna, Radha is Krishna’s friend and advisor in spiritual world. For some of the adherents of these traditions, her importance approaches or even exceeds that of Krishna. She is considered to be his original shakti, the supreme goddess in both the Nimbarka Sampradaya and following the advent of Chaitanya Mahaprabhu also within the Gaudiya Vaishnava tradition. Radha Chalisha mentions that Krishna accompanies one who chants ” Radha” with pure heart. Other gopis are usually considered to be her maidservants, with Radha having the prominent position of Krishna’s favour. It has been mentioned in the narration of the Skanda Purana that out of a two billion of gopis and queens, 16,000 are prominent. Out of these, 108 are important, and out of 108, eight are principal. Out of eight gopis, Radha and Chandravali are chief, and out of these two Radha is superior. Radharani’s superiority is given by Krishna’s flute, which repeats the name Radha. Between Radha and Rukmini, Radha is superior. It is also said that when lord Krishna brought all his consorts to meet Radha, they saw Radha’s face and declared her the most beautiful woman in the whole universe and that she would retain this position until the end of the universe as no one will surpass her beauty. All the gopis and queens of Lord Krishna are reincarnations of goddess Lakshmi but Radha is the eternal life energy of lord Vishnu.
Her connection to Krishna is of two types: svakiya-rasa (married relationship) and parakiya-rasa (a relationship signified with eternal mental “love”). The Gaudiya tradition focuses upon parakiya-rasa as the highest form of love, wherein Radha and Krishna share thoughts even through separation. The love the gopis feel for Krishna is also described in this esoteric manner as the highest platform of spontaneous love of God, and not of a sexual nature.
There is no question of envy in pure love.