Sex and lies

On Monday evening, I had a drink with A, a long-time female friend whom I haven't talked with properly for years. She is single, 50-ish, good-looking with a taste for insecure married musicians, preferably tall, dark and handsome.

We talked about affairs between married people, and she vehemently denied ever having an affair when she was married. Another female friend, C, told me that about 10 years ago, both A and C had both slept with the same man whom they had met via their childrens' primary school. C heard about A's affair from the man.

So, who was lying, and why?

A, to protect her idea of herself as a faithful wife?
Bloke B, to help get C into his bed, or as a boast?
or C, to get at A or to help excuse her own transgression?

In the last ten years:
A was widowed,
B is either dead or in a wheelchair with ME,
C has divorced and has also run a string of married men.

As for me, life is ordinary by comparison.