Is retaining a provider considered a felony or misdemeanor?

If all you mean is soliciting, hiring or engaging in the act of sex for gainful compensation; it is a misdemeanor (and a very insignificant one at that). If you mean "retaining" as holding her against her will; that would likely come under unlawful restraint, imprisonment or kidnapping which would surely venture into felony territory.

How about if you "retain" her for the purpose of "restraining" her, but of her own free will? lol

Have your way with her.