That'll happen. [ --when you're an egomaniacal, wealthy Gryffindor pureblood. Severus gives absolutely no credit to Sirius for leaving his 'cruel' family. He left his own brother to be killed and jumped ship right to another wealthy family willing to support his continued terrible behavior. But of course they were: their own son was even worse. ]

Edgeworth exists to shield him from all consequences and feed his ego. I have no idea what he gets out of the arrangement; my best guess is that he's so intolerable that the only way he can pin down a 'friend' is by bartering his services for Black's attention.

[ So that is. Not a very nice assessment. At all. But Severus can't figure it out - Edgeworth is a stupid, stubborn liar whom more people dislike than even Snape, and he's a bigoted bastard about magic. Why would any wizard put up with someone like that? The answer he can best put together is that Black, shallow prick that he is, is getting something out of it. ]