powershoweronthehour - "I think affairs are unfeminist in a similar way to porn- because they promote a view of women as objects for the use of men- "his bit on the side" "his piece" "his latest bit of skirt" "son cinq à sept" - as if the female affair partner is an accessory like a new set of golf clubs."
I find this a very strange take. As if the OW has no agency.
The descriptions you give are views of the OW, not of women in general. They would not apply to wives, for example.
Who promotes those views of the OW? They sound archetypal "male gaze".
Feathered - in your OP you posit an affair involving a married man and a woman:
"Do you think a woman who has an affair with a married man can be a feminist?"
There seems to be an assumption that:
a) the man is married to a woman
b) the woman involved in the affair is single.
Would the woman be any more or less a feminist if:
a) the man was married to another man?
b) the woman was married
- to a man?
- to another women?
c) the woman had an affair with a woman who was married
- to a man?
- to another woman?
If "feminism" were relevant in one scenario (circumstance) then it should surely be relevant in all possible situations?