This might be unconventional and go against fanon but I don’t care I’m clinging to this Angbang hc with both fists.
Melkor worships the ground Mairon walks on. He adores Mairon with his entire being, would do anything for him, trusts him entirely body and soul, and love love loves him. He doesn’t manipulate or play power/dominance games with him (if anything Mairon manipulates him). Everything he does and creates, he does with the hope that it will please Mairon and impress him. He lives and breathes to make him happy.
If Mairon said he wanted to abandon Angbad and go back to Valinor, the bags would be packed within the hour. If Mairon wanted a Silmarill to place on his crown, Melkor would rip all three from his and let Mairon pick his favorite, if not give him all three. If Mairon told him to bow, he would drop to his knees.
He loves Mairon so much and is very aware he would be nothing without him.