The stereotype is that men think only about sex. That stereotype works pretty well here. Yes, the important feeling of submission has nothing to do with sex. But sex is involved, one way or another, in most fantasies. Things that have nothing to do with sex are erotic if they involve being submissive.
So, for men, submissiveness is, one way or another, about sex. You probably should not leave sex out of your dominion.
If you set up certain times or occasions to dominate him, having sex is a good occasion. If you are going to control a little portion of his life, a good thing to control is how and when he has sexual release. This gives him a strong feeling of being controlled. It is also useful to you. He probably does masturbate. If you plan some exciting scene or event, you can ensure he is excitable and hasn't just masturbated.
There are several things you can do if you are controlling his sex life. One is denying him. This is a typical submissive game. The more you deny him, the hornier he becomes. The hornier he is, the more he desires sex, which you control. So he is more in your power, which he finds exciting.
Another is that if you control his sex life, you can use sex as a reward or punishment.
Finally, you can be kind. You can try giving him permission to masturbate, if that makes him happy. You can find a rate of sexual release that works for him. The caring strategy is to enthrall him with as good orgasms as possible.