Silmarillion - Chapter 01 - Of the Beginning of Days

[Raynor]

It seems to me that Melkor loved the Darkness.

Hm, I disagree to an extent:

Originally Posted by Myths Transformed, II, HoME X

As a shadow Melkor did not then conceive himself. For in his beginning he loved and desired light, and the form that he took was exceedingly bright; and he said in his heart: 'On such brightness as I am the Children shall hardly endure to look; therefore to know of aught else or beyond or even to strain their small minds to conceive of it would not be for their good.' But the lesser brightness that stands before the greater becomes a darkness. And Melkor was jealous, therefore, of all other brightnesses, and wished to take all light unto himself.

the Valar do not diminish, even after healing many hurts and making Valinor, etc

Not quite, or at least, not on the long term:

Originally Posted by Notes on motives in the Silmarillion, iii, Myths Transformed, HoME X

The Valar 'fade' and become more impotent, precisely in proportion as the shape and constitution of things becomes more defined and settled. The longer the Past, the more nearly defined the Future, and the less room for important change (untrammelled action, on a physical plane, that is not destructive in purpose).