A lot of the amount could well be interest that has accrued which would make me almost a mad as any of the other reasons as the interest and the position you are now in would have been more avoidable if he had been open and honest
If the renovations were £40k, you could get to £100k+ debt over 4 years with £1000 over spend a month at 5%
It is still an eye watering amount of money but equates to more like £30 a day rather than the £300 another person calculated.
I wouldn't accept taking over the finances this is his mess to sort out. I would request full transparency and to be involved in all conversations in terms of engaging with payment plans and sorting everything out, he's to take responsibility for it. The first thing for him to do is to go through his possessions and sell any with value.
I wonder if it started around the time of the renovations and he started spending more as if you are borrowing £30k what is an extra £1000 on buying whatever it is he's spending the money on and it's snowballed.
What sort of contact do you have when he is away, would a video call be possible? I think right now you need to have full oversight over what the debts are, which are the ones that will cause the biggest problems and go from there.
We have a spreadsheet which covers all the money we have. All our outgoings are on one tab, our savings on another. It has the details of mortgage, dates when deals expire and we both update once a month and once every 3-4 months we go through it together to check on where we are. I would look at doing something so that there is a track of his spending and debts for him to complete but you have oversight so you can see it's moving in the right direction.
How do you usually manage money with in the relationship? Would it be worth mirroring what you ask if him? I don't need permission to buy things but I would say I talk to my partner about 98% of what I buy. It's not in-depth but can be, Child has had a growth spurt. I've found leggings, t shirts and PJ's in Sainsbury's. What do you think? Often "fine", some times would she want shorts for when we go away or mums bought some PJ's. In many ways it is unnecessary but also it means we have a very open dialogue about money and spending and means that the big money conversations are easier.