Alastor had Lucifer on a leash. Living like that made Lucifer feel trapped so he often growled at Alastor. But Alastor found him adorable and didnt let him escape. Lucifer was always trying to bite Alastor, but Alastor would put a muzzle on him which Lucifer hated

Lucifer didnt like Alastor but he did like cuddles and praises so he beard the annoying human aka Alastor