I think "father" Argus cut him loose to let him branch out, get stronger, and raise higher than he ever could. I think this because the constant mention of C rank. Thief and him can go no higher than that. So he used this as a good opportunity to free the protagonist from the responsibility. I want to believe we'll find out later that Thief was kicked out down the line.
As for Bitch, I'm sure she'll come crawling back once the protagonist has made a name for himself and his party.