Very well said, gives a lot of interesting things to think about.I think somewhere earlier I commented that this is not a common female fantasy, to watch her other half do another woman. When surveys on sexual fantasies are performed, we are invariably in a conscious form, and certainly this fantasy is not visible.
A fantasy which is similar but certainly not equivalent, and is more visible, is for us enjoying watching a woman being fucked (not by the husband). Just the idea of seeing a woman getting fucked. I did mention before that i used to get excited hearing and watching my roommate at university getting fucked. Yes, this is not uncommon, and it surfaces mostly in group sex, in the heat of action, some women do enjoy watching other women getting fucked, but not the husband.
There exists definite reasons for a woman to seek a threesome with her husband and another woman, and enjoying seeing him do her. These are mainly in the subconscious and they rarely surface. A prerequisite is for the woman to be capable of completely separating love from sex. A complete separation. Also being sure that her hubby too can do the other woman without the possibility of emotional involvement. This is premordial. This is in the conscious. As for the subconscious, a woman who is very proud of the sexual prowess of her husband, may want to show another woman how good he is, and usually she wants to see her husband ravaging the other woman. At times this desire surfaces when two women are arguing about how good their husbands are. The other reason relates to women who believes that women are "whores" or "sluts" (metaphorically speaking) and she wants to see her husband punish that whore. This desire may surface when a particular woman acts like a slut in the presence of a woman who subconsciously enjoys this fantasy. In most cases it may relate to close friends, with the woman desiring to see her husband fuck her "slut" friend and punish her. The third reason is when a woman is incapable of satisfying her husband and wants to see him with another woman, but mainly wants to see how the other woman is satisfying him. The fourth reason is the woman counterpart of male cuckolding, with a woman enjoying and getting gratified in being humiliated in seeing another woman satisfying her hubby.