Hold on, so this is nothing new to him?
This paints a slightly different picture.
This is a man with terrible judgement around money. He was in debt already when you got together (first mortgage application declined due to that). Do you know what the total debt was then?
It sounds like he has done absolutely fuck all about it since, didn’t bring it down one bit and if anything, it has only skyrocketed.
At this point, to me, question where the money went becomes secondary… what becomes clear is, he is a very high risk person to be financially tied to. I can’t stres this enough.
As his mum was the same and debts predate you, this is entrenched deeply in him. He is not going to become a different person overnight (heck, even over a year).
All the little spends on bets, trading 212 (which i know nothing about apart from other posters writing about it), points at someone with a gambling mindset. This is the same as addiction.
By all means, dig around, ask to see more. But if i were you i would be mentally drawing a line. If i were you this would be enough for me.
Whatever future is ahead of you alone, it is much scarier to be financially tied to a person like him. You will forever be wondering what other financial disaster is around the corner.
I am so sorry you are in this situation, i feel sick just reading about it all. But you can and will get to the other side.