Control

There will be times when you or sub may not be in the full control mood but you can still allow him some rewards....
IF he has dutifully worshipped and obeyed you he may wish to lick you palace or indeed you may wish to suck his manhood to give him ultimate pleasure but you MUST only do such things when you FEEL he has deserved this. He must be aware that you are boss and have you tried chastity device to keep him under total control and say that he cannot be freed until he has proven his worth to you. you may also wish to dress him up, x dress REALLY lets them know who is in charge plus I guarantee it's a turn on for you.
My sub is older and at times claims he cannot take the pace, however I am wise to this and merely play with him ie whip, dress him, pee on him and allow him to recover but only long enough for me to enjoy the full services of my slave. Yes we all have times when we are maybe not 100% up for it but there are many tricks- you may ask your sub to go off and purchase some sexy gifts for you, get him to do chores etc.
I am sure that you just keep experimenting and you'll still have great pleasure and allow some rewards for your obedient sub!! mix it up and don't give any clues away he will NOT know what's hit him.

On evenings where you do not feel up to doing a full scene,
perhaps you might "allow" him to please you visually without
touching you (thus you are a voyeur and not a participant; you
can sit back and relax). Make him masturbate and try to keep
your interest (he has to "earn" it) while you look at a magazine or
take a bath. Make him wash your back and pamper you, bringing
himself almost to the point of climax several times. When you are
done with your bath and after he towels you off, allow him to
release himself into the tub, and then clean the tub while you get
in bed and get some much needed shut eye!

The shower scene from the scenes to play page would be good
for that situation as well as doing a kind of how long can you go
without me challenge. If your tired one night say, if you can still
be a good boy all night and all day tomorrow then I will reward
you beyond your wildest dreams. Tell him some things you'd be
willing to do to him the next day if he's only willing to wait. Make
it so that he's so eager for tomorrow he's happy to wait.

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Quit bitching, you know you like it.