Hi lisazoe
Welcome to the family!

It's his Mother. He told me from the get go about how his mum has always controlled him in life and his siblings and how she has these rages at them when things don't go how she wants it to.
Would you say his mother uses/used things such as fear, obligation and guilt to intimidate and control your partner and his siblings? If so, you might find the following article interesting:
Fear, Obligation And Guilt (FOG): How We Allow Loved Ones To Control UsUntil the day she found out that we were actually a couple she thought I was a really nice person.
That changed within a split second.
Suddenly I am (apparently) controlling him, preventing him from seeing and communicating with his family, trying to get him to parent my child ( I have a daughter from a previous marriage), I'm taking all his money despite the fact I have a job and earn more than him, use and take all his possesions which so happen to be mostly mine from my house, taking away his dignity, controlling his career to suit my own purposes... .the list goes on and on and on... .
I am 12 yrs older than he is (sadly I've just turned 40! and he is 28) and as you can imagine this doesn't go down well at all. She has outright lied to my partner saying that she knows why my ex and I broke up and its because I'm such a bad woman etc etc... .my ex and I have a good relationship which is actually a good friendship which we have built on the basis of meeting the needs of our daughter and we all get along extremely well.
How did this extreme shift in the way she views you make you feel? Her behavior as you describe it here sounds very much like the BPD behavior known as 'splitting':
Splitting refers to a primitive defense mechanism characterized by a polarization of good feelings and bad feelings, of love and hate, of attachment and rejection.
Splitting is a powerful unconscious force that manifests to protect against anxiety. Rather than providing real protection, splitting leads to destructive behavior and turmoil, and the often confused reactions by those who try to help.
Some degree of splitting is an expectable part of early mental development. It is seen in young children who, early on, press to be told "Is it good?" or "Is it bad?" We hear their frustration when we answer, "Situations are more complicated" "Yes, I know all that," they say, "now tell me, is it good or is it bad?"
Normally, mental maturing advances the ego's ability to accept paradoxical affects, and to synthesize and balance complex situations.
... .
Individuals suffering from borderline personality disorders live in an immature psychological world, fueled by certain constitutional vulnerabilities, where they attempt to shield themselves from conflict and anxiety by splitting the world into all good and all bad. Although this produces an sense of psychological safety, in fact, it renders relationships fragile and chaotic and drives away the very people who are so badly needed to provide stability in the borderlines life.
You can read more here:
BPD BEHAVIORS: SplittingMy story will typically reflect so many others on here. It is so interesting to read and see what tactics others have of coping and dealing with these BPD people.
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I look forward to reading more info and finding support and help along the way.
The old cliché of 'knowledge being power', really applies to dealing with someone with BPD (traits). Reading the stories of other members and how they deal with things, can be very insightful and I definitely encourage you to keep doing so

Have you shared with your partner that you believe his mother might have BPD?