oh, fgs
OP, why are you being made to feel guilty about "stopping him having any friends" ?
Are you trying to be a "cool" wife ?
I suggest you find your inner "uncool" and give your husband an ultimatum. His "strong bond" with another woman, that he is openly planning to "strengthen" in RL...
Or his marriage
I am sure that not many people will agree with ultimatums, but if you have repeatedly told him this makes you uncomfortable, he is not listening to reason
If i dredge my mind for an altruistic reason for him meeting this clearly vulnerable woman, I might just come up with the idea that he seems himself as her "rescuer"
A situation like this is an absolute minefield, and at best he is being spectacularly naive and appears willing to bulldoze his way ahead regardless of your feelings.
How strongly have you worded your concerns, btw ? A quiet little "I am not sure I am comfortable with this" is not strong enough. You should be ridiculing his cliched midlife crisis, tbh. What a weak and deluded man.
If you think giving him am ultimatum will send him off to her anyway, you have your answer, don't you ?