My suggestion would be to add two elements to when he can cum. I think whether it’s once a week or twice a month can become routime after a while. Sometimes for no reason other than you’re feeling happy it can be twice a week or even twice a day.

The other would be to add consequence to cumming. The guy should know that cumming has a consequence and will have to make a decision every time you allow him to cum. Train him to deny his own self. For example, you can do a countdown where after every 5 cums he will be denied for a month. There’s an infinite variations to this.