Answer
No, Radha and Krishna are not one soul. Krishna is the Supreme Soul, the Supreme Personality of Godhead, whereas all living entities are individual jivatmas — separate, eternal souls. Each jivatma is an individual spiritual being with a unique relationship with Krishna.
Radharani does not belong to the category of ordinary jiva souls. She belongs to Krishna’s internal potency, His spiritual energy. The internal potency manifests in various forms and expansions, all meant for Krishna’s pleasure.
One aspect of this internal potency is the hladini-shakti, or pleasure potency. For Krishna’s pleasure, many transcendental personalities exist — such as Srimati Radharani, the gopis, Mother Yashoda, the cowherd boys, and other eternal associates of Krishna. Krishna engages in loving pastimes with all these personalities.
In these spiritual pastimes, both Krishna and His devotees experience transcendental bliss. Each one tries to please the other. Krishna gives pleasure to His devotees, and the devotees dedicate themselves to giving pleasure to Krishna. This loving exchange is the essence of spiritual life.
Therefore, Radharani is neither an ordinary jiva soul nor identical with Krishna in the sense of losing individuality. She is Krishna’s internal spiritual potency, eternally engaged exclusively in serving and pleasing Krishna.
Regarding the question of Radha and Krishna’s marriage, there are indeed pastimes in which Radha and Krishna are married. Similarly, the marriages of Sita-Rama and Lakshmi-Narayana are also divine pastimes. All such activities are transcendental lilas.
Lakshmi, Sita, and Radharani all belong to the Lord’s internal potency, and each serves Krishna or His expansions in unique transcendental moods for His pleasure.
These divine marriages and relationships are not material activities; they are eternal spiritual pastimes meant for loving exchanges with the Supreme Lord.
Ultimately, the soul itself is spiritual by nature. The pure soul does not act materially but participates in spiritual enjoyment through loving devotional service and relationship with Krishna
