So he's in Chastity, but does he know why? He may think this was his idea, but remind him that it isn't anymore.
Let him know how much you are becoming accustomed to having the key and how you are enjoying the benefits.
Make a habit of reminding him that you prefer to keep him in chastity since you discovered his love for panties, which obviously makes him a sissy...and in turn means that he shouldn't have any use for his little cock anymore since you will be treating him like a girl. Tell him that it's also better to have his useless cock locked up since his cock is so small and insufficient.
Remind him that he's the one that started it and wanted it, but he should've been careful what he wished for.
Also, since his little cock is locked up and unusable, tell him you'll be looking for other cocks to satisfy you and he'll be able to watch you get real pleasure and satisfaction from a real cock while he's comfortably locked up and denied.
The point here is to make a list of reasons why you keep him in chastity and to constantly tease and remind him of them.