Train him to eat his own cum.

1.  If you allow him to cum inside you, he should clean up his mess
 2.  Equal treatment for the times he has cum in a woman’s mouth
 3.  Reinforces his submissive role and obligation to serve you
 4.  Opportunity for you to orgasm again and cum in his mouth
 5.  Blissful display of post-coital affection and tenderness
 6.  Normalizes him to the taste of semen.