@MyKingdomForBrie "Surely you would first approach your friend and exhort him to be honest with his wife before speaking for him?"
To be honest, in this situation, as I have said repeatedly, I would leave it alone. When you say that you think the OP should approach her friend, is she going to convince him to behave well?
I am not condoning what he is doing, it is slimeworthy.
If they were not undergoing IVF and if the woman were a good friend or relative I probably would feel compelled to tell. But I would be aware that my relationship with the 'cuckolded' partner may be at risk.
Is it completely clear he is having affairs with other women, or just saying he wants to?
In this situation, I am not sure it would be in the woman's best interests, at this time, to spring this on her. The OP is not responsible for telling her.
Clearly we all have different options, which is fine, but having had IVF in my thirties I am afraid pretty much nothing, not even infidelity, would have been more important at that moment than completing the treatment. And a stranger coming and throwing a grenade into my life, would have been most unwelcome.
The question I am trying to answer is probably not the OP's question. She has asked 'Would you want to know?' and in all honestly I am not sure.
But I am answering a different question. I am answering "Do I think this man's wife would want to know?"
And my gut feeling is, right at this moment, she would not. But, as ever, I may be wrong.