If you and her are having high quality sex, it actually increases her chances of becoming a slut for her future lovers. But if sex is not much good between you, she often does not realise how good it could be with others.
The stronger your marriage, the easier it is to persuade her that you wish her to have your special gift of extra-marital sex as a reward for being such a loving wife. But you have to show by your actions in helping more about the house, that you are not using it as an excuse to sneak off and swing with other women.
You want her to accept your gift - she has not offered you the gift of fucking other women, so sometimes you can offer to wear a chastity cage to PROVE you won't fuck behind her back........that you do not expect her "gift" in return.
Wife takes lovers, husband remains monogamous and shows respect to her lovers, marriage remains intact, wife sees everyday evidence that her husband wants only the best for her, and his happiness cannot feel complete unless his wife is having a wonderful social life meeting new friends of her own choice. FINAL RESULT = happy wife feels grateful her husband is so understanding and supportive of her primal needs.