@TedMullins
I agree and that is your perogative.
If you wish to have a relationship whereby you explicitly explain you will not be putting partners above all others, that is your choice.
Where this falls down is I believe this is probably quite one sided, op has prioritised her husband in their marriage and he has not. It's about the agreement, the contract, what you both want and for some time now this agreement has been one sided.
The op's fears about this woman are her deepest fears about abandonment, humiliation, respect and realisation she may be taken advantage of, that another woman has power over the dynamic of her relationship, that this woman comes before her.
Not a pleasant place to be or feel when in a marriage which you believed to be equal, and what does he do, he makes it worse by confiding with this friend further deepening their bonds and allienating op.
Now what would be an example of this being turned arround, for instance maybe op's husband has a small cock and it's his deepest insecurity that anyone would find out, god forbid that op should critisize his performance. Now op tells a trusted male friend, he supports her, sympathising with her for her lack of being satisfied.
Do you not see some support makes situations worse, they are not beneficial to a marriage, they are actually harmful and gaslighting this woman saying she should suck it up in the name of her husband having a lovely friend is not kind.
Op needs to find someone who has her back, supports her and also protects her.
What is the point of this man, he's giving all the strength to the ow, and I would say the many posters on here who believe their male friendships are just as important as the relationship their male friends have with their wives are very self important, ignorant and selfish, not to mention cruel.
They wouldn't like it done to themselves.