If he ramped it up so fast yet has nothing to show for it; no expensive hobbies, holidays, flashy wardrobe, showy cars, and he doesn't pay all the bills ...
Where's it gone?
Does he have any dodgy friends, mysterious visitors, phone calls, unexplained absences?
Drugs and gambling can get him and you into nasty company.
Prostitutes can give him and you STDs.
Is he a heavy drinker?
You need to know the truth.
Ask to see evidence that he paid off the debt with his mother's money. If he did, it exists.
And look at ALL the other evidence. Phone/mobile bills, credit card spending breakdowns, bank statements. The credit card bill will show you where it all went. (Mine reveals a ridiculously spendy coffee shop habit.)
If he shreds paperwork immediately, he's hiding something.
Get him to obtain paper copies to show you, if he usually only does it digitally.
If he refuses to show you, he's been lying and it's going elsewhere.
Your first suspicions have been proved right. Now your and your family's wellbeing is at stake.
Tell him if the marriage is to survive, I insist on transparency, clarity, honesty, openness ... These are non negotiable. These are my boundaries.
Get an appointment with a solicitor and find out your situation re your rights.