A true Cuck will be totally satisfied not to be involved while you fuck another man (a bull). He need even be present, and when you get back with him, whether it be in the next room, or back at home, his main goal is to "Reclaim" You. a LOT of Cucks will live for the Cream Pie that you feed them when you are finished, and some Cucks are caged and only get to fuck occasionally.
Your guy is not a cuck, for quite a few reasons, but mainly because he is competing with his 8", which a cuck would never do, regardless of his size, the Bull is totally in control of the wife. But this is a very grey area, just saying.
If I were you, I would just swing a leg over his face and tell him that you want him to lick you clean after another man (Bull) has cum inside of you. All he can say is "No!" But if you can get him to lick that cum out of you, you are WELL on the way to training your cuck..