Depression. The fifth stage of grief.
Crowley did nothing but whine about himself, but what else could he do? Since the aborted Armageddon, Aziraphale was his only companion. He had no other... friends or acquaintances or contacts. No one mattered more than Az- the angel. His angel. Why had he left...
Crowley just wanted to lock himself away somewhere and never leave this particular place again. He was no longer needed anywhere. The Bentley might suffice. Or his apartment, now that Shax had returned to Hell. He could simply stay there for eternity with only his plants and Queen's music.