Slave always wants to cum, but he is never allowed to unless I let him.. For me it's fun to tease, edge, and deny him for hours and days.. I love keeping my slaves horny and frustrated..  I need to be sure he has not been cumming when he's not supposed to, so I'll be testing him by how much edging he can handle until he cant stand it.. Later, when I sit on his face and make him sniff my ass- I know he's not going to be able to last very long..  I suppose he passed his test, but still gets a frustrating ruined orgasm.. That's enough of a reward from me.. Hehe