I'm a non-muslim, but I have some experience of being in your ex-partner's position, i.e. having a mad, controlling mother. I would say the emotional abuse was to a lesser level that that of your partner's mother, although some of the details are eeriely similar. (We're talking not getting my own bed until I was 16, abusive phone-calls to my friends (when I was an adult who'd left home) because she wanted me at her house. That kind of thing.)
Based on that, I'm saying NO. I have deep sympathy for your ex-partner, and he is truly in an unpleasant situation, and always has been. But his mother should not get the opportunity to get a hold on your baby, any more than my mother should get hold of my children.
If your ex-partner isn't strong enough yet to protect your baby, then it's your job, just as it would be my husband's job to protect our children, if I fell back into old patterns.
The power an abusive parent can wield is difficult to describe. I look at my life, and I think, "Well, why didn't I do that? She was hardly holding a gun to my head! How could she have stopped me?"
I'm still not fully out of those patterns. The big decisions, like telling her I will get married/live where I f*ing well like, yeah.
But for seemingly smaller things (that are actually pretty damn big, when you think about it), I do what I'm told and only realise later on.
Here's an example, which I am deeply, deeply, deeply ashamed of, which led to the realisation of exactly how far I have to go.
I went on a shopping + playground trip with her and my pre-verbal toddlers. It was okay for a bit. They had a small packet of baby snacks before the play area. Then I thought that it was time for them to have a proper meal. She said, "why? If they were hungry they'd be crying, and they've had that whole packet of snacks". I couldn't explain why I was convinced they were hungry. She said, "honestly, you're always taking them to eat If they were hungry, they'd be screaming."
Well, the rest of the trip wasn't so good. They were constantly on the verge of being upset, and my mother was cross that they weren't happy to sit and watch her trying on shoes, as they normally would have been. (Very content little people usually, my boys.) I had to keep moving the pushchair to give them new things to see. But I didn't realise they were hungry, because my mother had told me they couldn't be.
Once I was on the way home and there was nothing to distract them from their hunger, out from the malign influence
, then they began to scream for food.
And then, everything clicked. They were hungry, and had been for so long, and I had allowed my mother to impose her issues with food on them, without even realising! Something I had vowed I would NEVER do.
My only explanation for my stupidity (not an excuse, for there really is none- my children should not have suffered because of my psychological problems, or hers), is that I had never consciously associated the toddlers' behaviour with whether they were hungry. Up till then, I had simply "instinctively" known when they got hungry and fetched food for them. So, that day, I was unable to justify myself in the face of her justification, and thus fell into automatically trusting her over myself.
I hope that you understand the story I'm trying to make.