[Formendacil]

Here's the pertinent quote regarding the forgiveness of the Valar:

Then Manwe granted him pardon; but the Valar would not yet suffer him to depart beyond their sight and vigilance, and he was constrained to dwell within the gates of Valmar. But fair-seeming were all the words and deeds of Melkor in that time, and both the Valar and the Eldar had profit from his aid and counsel, if they sought it; and therefore in a while he was given leave to go freely about the land, and it seemed to Manwe that the evil of Melkor was cured. For Manwe was free from evil and could not comprehend it, and he knew that in the beginning, in the thought of Iluvatar, Melkor had been even as he; and he saw not to the depths of Melkor's heart, and did not perceive that all love had departed from him for ever. But Ulmo was not deceived, and Tulkas clenched his hands whenever he saw Melkor his foe go by; for if Tulkas is slow to wrath he is slow also to forget. But they obeyed the judgement of Manwe; for those who will defend authority against rebellion must not themselves rebel.