You have asked your DH not to divulge your disagreements.
His mother is asking him to do the opposite.
He does what his mum wants.
He is choosing her wants and desires over yours.
He blames his mum when he is with you. He probably blames you when he is with her.
Has he ever blamed his mum for tightening the screws to get him to open up when you are present? Mentioned in front of her that he doesn't want to discuss your issues, but she won't let up?
I'll bet my last dime he hasn't.
Ask yourself this OP.
Could you feel loving towards someone who was making your DH extremely unhappy?
Could you perpetuate the situation by feeding that person negative shit about your DH?
You seem to want to prove to MIL that you are not this unreasonable spiteful person, that you don't want to give her a reason to think you are deserving of the way she goes off on one about or at you? Why bother? Who cares what MIL thinks?
You will never ever control what she thinks, of you, of him, of your DC, of anything!!
Let her think whatever she chooses to think.
Focus on you, what you think, what you want, what you feel.
She's got a very enmeshed relationship with both of her sons. Neither sons sound like they can formulate their own opinions.
I really don't understand how you can feel loving feelings towards such a weak man, so weak that he can't or wont stand by you. You must feel so lonely in your marriage.
I couldn't trust a man like that. I'd be on tenterhooks every time I opened my mouth in case he repeated my words to the people who dont like me.