I need help. My mother,sister, and I are very close and we have always been open about sex. I've been married for years to a good guy. My mom is getting a divorce and hasn't dated in over 6 months ...
I hope this is your idea of a sick joke, but if it isn't then I have this to say:
Where is your mother's head for suggesting such a thing? And yours for considering it?
Absolutely not. And if you are going to try and fool yourself with the argument, 'What harm can it do?' then let me ask you this: If you do not FLAT OUT tell your mother that she's got a screw loose and there's no way in hell what she proposes is going to happen - and if she DOES have sex with your husband, 'just once' then what is to stop them from continuing to do it?
And then what if your son gets older and your mother tires of your husband's stud services? Will it be okay with you if she 'teaches' your son 'what every man should know?' He is 13 now and you didn't boot her out of your house when she proposed showing him how to masturbate!
Get a grip! You owe your mother RESPECT and LOVE. You do NOT owe her a sexual partner. In fact, based on the conversation as you report it; you no longer owe her any respect, either.
If you feel inclined to do ANYTHING for your mother (and personally, I wouldn't) then locate and set her up with a nice SINGLE man. And if you don't know any, pop for an escort service. She can meet a nice guy that way - and one who will most likely be willing to 'earn' his pay... they're called gigolos.
Oh, and one more thing. You need your mother to watch your kids so you can "continue (to have a) social life?" Now that I think about it, you and your husband and your mother all deserve each other. Just do the rest of us normal parents a favor first, would you?
Find a new home for your kids where they can be raised with integrity and morals, by someone who loves them enough to sacrifice for them instead of passing the buck to someone who's not only mentally deficient but as spoiled as you are.
You and your mother need mental help from a qualified psychotherapist. Please get some before you ruin your children's lives as well as your own.