In my marriage, we had many on both sides. We had them over to dinner and knew of their travails. We gave them money and support.
But if Mrs. Cain was not privy (as is currently being reported) to to that part of his life...
First of all it's opposite “SEX”, not gender.
It is not possible for a man to have a female as “JUST” a friend. Many times these relationships end up in marriage. A MARRIED man should NEVER have a close female friend. This is fraught with danger. These relationships usually end up in divorce.
The male sex (not gender) drive is very powerful. A few too many drinks, a vulnerable moment when she needs comforting....DISASTER!!!!
Don't tell me “oh, I've had a female friend for years Blah, blah, blah. You are playing with FIRE!