It's almost like as soon as he begins to settle in a job he decides to leave to try something different.
I think this is most likely to be related. The longest I have worked anywhere is 3 years and that was in a job that I was very over qualified for.
I've been in one of my current roles for just over 2 years now (I work there a couple of days a week) and the drive to leave now is huge. I feel like I can see colleagues 'going off' me the longer I'm there. I hate it. It's horrible. It makes me want to hide from them and sometimes I do.
Surely a mother should want to do anything to support their child.
You'd think wouldn't you? In my case, mine sabotaged everything. It was proper stately home stuff - we went to NT properties, I had ballet lessons as a preschooler, swimming lessons, music lessons... but that was all because she was a good mother providing all those things and very visible to others (which was the important bit). The problem was me.
She sabotaged everything: friendships (would lock the front door so I couldn't leave to see them or would refuse to allow me to phone them etc for arbitrary reasons and they eventually stopped trying; she told me they didn't like me anyway because there was nothing about me to like and then used the fact they no longer made an effort with me as proof. I became defensive and avoided making friends to protect myself from the hurt); my education (A level and university); constantly told me I was an unfit mother; undermining my parenting and attempting to get a SW involved eg for a situation she had engineered. When my eldest had an obvious SN, she bullied me out of seeking a diagnosis with the faux concern that it had been my poor parenting that caused it and 'concerns' that they'd take him away.
Despite her very best efforts (and I have to hand it to her, they were good), no one else has ever expressed a concern about my parenting and my children are delightful people with whom I have an excellent relationship (I decided to just parent in the opposite way to her - whatever she did/would have done, I did the opposite). I returned to university in my late 20s as a single parent and got a first class degree (which she hated). I later returned and got a pg prof qualification. She attempted to undermine and sabotage that but, fortunately I had just enough support elsewhere to resist it. My child was diagnosed with an SN and got the support he needed - well almost. I still can'tdo relationships or friends very well and I
I have been NC with her for 6 years now. Ironically after all the years of being 'concerned' about my 'stability' and 'mental health', her hatred of me meant that she did something regarding my children that triggered a safegaurding alert. So she got her SW wish after all. Except that they declared her a risk to the children and said they'd close the case if we agreed to NC.
Sorry this is so long! I'd always assumed that with her out of my life, I would have a normal life like other people - I'd have the career I trained for, friends, a relationship. But all the freedom from her has done is expose just how badly she broke me fundamentally.
It has been a horrifying revelation. This wasn't just something that existed between her and me; this is something that runs through every part of me and affects everything. But it's like a slow dropping of many pennies. If your husband is talking about this now, it might be that something has triggered it for him.
Don't confront his mother. It will do no good. You won't like the response, I can guarantee that.
All you really need to do is be there for him. Listen. Even if what you hear is hard. He isn't telling you now because he wants you to say "what a cow" and go and sort her out for him, but it's probably the first time he's collated it all in his head. He needs to articulate it, get it in some kind or order, make sense of it, realise the enormity of it. He will begin to realise that even some of the things that he always assumed were ok, we also just more subtle forms of abuse. The main thing he needs from you at the moment is not necessarily a solution, but just to be heard and have his memories and feelings heard, recognised and validated.
Give him the space, and the forum, to process his thoughts and feelings. That is the biggest help you can be. If he goes for therapy before he is ready, it won't work for him.
He is very lucky that he has you for support 
