The penny has just dropped! Like me, Jean-Paul Sartre must have had three ducks in his garden, and that gave him the idea for Huis Clos.
In my case, there is the Cuckolded Duck, the Lover Duck and the Lady Duck (the one now sitting, presumably on fertile eggs). This morning, while she continued to sit, the TWO males were side by side at the edge of the pond, apparently the best of mates.
So, this is how I see it:
Lover Duck is in love with Lady Duck, Lady Duck is in love with Cuckolded Duck, and Cuckolded Duck is in love with Lover Duck.
Or something like that. It's confusing for me, so goodness knows how the ducklings will cope....