Would Melkor be jealous of Celebrimbor?
Melkor would probably be angry at first that I turned my attentions to someone else and forgot that he was in the Void. But Melkor knows that I am his. He’s always known that.
Truthfully I was always the more jealous one. No one was allowed to even look at Melkor. And if Melkor looked at the shiny of someone else for a moment, my rage burned for months. Honestly my jealousy grew after he returned with the Silmarils because I always feared he would choose them over me. But then at the end of the whole Luthien incident, he proved to me that I came first. I was scared to return when I heard he’d lost a Silmaril because of my failure. But he found me. And his only concern was my wounds. There was no rage in the face of his fear of losing me. And then, at the end of the war, he chose to face the enemy alone, even knowing what they’d do, in order to save me. He proved his ultimate love for me. I had no reason for any jealousy I’d ever felt.
So to your question, I do not believe Melkor would be jealous, though he might be angry. I am his and he is mine. Whatever, whoever else there is, nothing will ever change that. I will remain ever his to the very end of the world.