Q: Quickie
For many cucks, being a cuck does not have to mean being completely cut off from their husband/wife's sex life. Not only may the cuck be allowed to watch or even 'clean up', sometimes your hotwife/hothusband may still want to have sex with you. Of course, it will never be the hot, passionate sex they have with their bulls, but it'll be quick and efficient. A quickie to fulfil an immediately physical need. Maybe they just need to get off and no bull is available -- especially when they tend to sleep around, finding the right date can be exhausting and sometimes they're just not in the mood for that.
Of course, don't count on shooting your load or even using your dick. Most likely you won't even get unlocked. If they want dick, they'll just attach a strap-on over your locked and useless dicklet. Or, maybe they'll use your pussy, or make you go down on them. Whatever they chose, what's important it that it won't be passionate. It won't be love making -- it'll be masturbation where their masturbation aid just happens to be human and their cuck. And, most importantly, you won't get to cum.
Coming to think of it, a quickie like this is probably more humiliating and degrading than watching them with another man. Yet, you're just happy to be of service!