Unfortunately (or fortunately depending on your point of view), Lucifer earthly job of law enforcement consultant left not much time for Amenadiel to have constant and sustained dialog with his brother. The skilled heaven-negotiator resorted to a different approach, talk to Lucifer’s confidant, Mazikeen (Maze), to help him get through Lucifer. Maze agreed. Their frequent interactions towards the objective opened up the opportunity for the angelic creatures to get sexually involved. It was naturally sweet (pun intended) for both but the constant fight between good and evil rendered it impossible for the relation to last. They both resorted to adopting their eternal position, fight one another, thus making succeeding into getting Lucifer back to Hell a more elusive proposition.
After much time had elapsed and Hell was still without a king, God knew Amenadiel must have run into difficulty to convince his brother to “do the right thing”. Although the Almighty would naturally extend the skilled heaven negotiator time to complete the mission, he learned of Amenadiel’s indiscretion (with Maze); Irritated, God decided to strip him of his wings, thus prevented him from returning to Heaven until the job was done, however long that would be.