Really difficult to describe but will try my best.
Now Ex DH of 30 years, met when i was 21 and he was 32. We are from fairly different family backgrounds, but before I go further I will say that he has never shown prejudice to any social group. That kind of thing has never seemed to interest him at all.
I was born into a good deal of privilege, he wasn't. We both came from stable families and never suffered any early trauma. He did not grow up in poverty but had much less choice than I had, and left home at 16 due to arguing with is parents as he did not want to get a job. He joined a kind of arty counterculture and dropped contact with them.
I met him quite young and we seemed to have a lot of things in common, although looking back I am not so sure. My family liked him and were very open minded when I moved in with him but advised me to be careful of putting my education on hold. After a few years I applied for uni and received many offers, my chosen one happened to be at the other end of the country. He really didn't like this and told me the relationship would not survive the distance. He even went so far as to suggest having a child, which was crazy since we had both decided we didn't want any.
Unfortunately I turned the place down and relocated somewhere local to him instead. I felt as if he gritted his teeth through most of it, but never said anything. During most of these years my parents were incredibly generous and funded my education/home costs. And this brings me to the weird bit -
The 'negging' thing has only become apparent to me lately, in retrospect. During that 30 years he always described me (and 'us') as 'struggling', as never having had access to any kind of privilege, and that we didn't fit in to society. I thought this was unusual but never really questioned it. As the years went by I slowly took on his values and perspective. He chose low paid work and terrible housing, which my family advised me against, but I loved him so went along with it. For many years I did very little with my degree. He always favoured his friends to mine, so slowly people from my own background lost touch.
A few arguments over the years brought this up, and he would insist that we 'began from nothing' and 'didn't have the options' other people did. If I mentioned my background he would absolutely refuse it, saying my family were just like his, but with a car 
Over the years I have come to accept that I was indeed extremely privileged and had many advantages at my feet, with an endless safety net and security even going into my 40's with some inheritance.. His denial of this seems so thoroughly weird to me, and I can't think of why he would do that, since he does not seem to have any kind of class prejudice at all. His sister and brother are more the other way - they both used to rib me constantly about my speech and behaviours.
Unfortunately the relationship left me confused and uncertain of myself, nothing new I know, but it has been difficult for me to re-establish my own memories and awareness. I now see myself as having lived a life of struggle even though I really really haven't. He even insisted my inheritance was 'small fry' and useless to me, which I am sure it is compared to many.
Why would someone do this?
I have heard of people having cultural clashes but this was like a whole scale denial, one that I stupidly went along with. In a way it is like my confidence was slowly stripped from me, but because there was no overt abuse I couldn't see it happening in real time. He always got on with my family and they supported him often, yet his family largely didn't approve of me due to a belief that I would hurt him (no idea why) and that I was' laa-dee-daa'.
WTF does any of that mean? is it at all common? Am sorry it is so long, I tried my best to condense it.
is it a kind of negging? It sure feels like that now.