About 2 months after we got married, DH filed his taxes (he's a US citizen). He hadn't filed them for several years before - said he couldn't be bothered (very naughty and he would eventually have got caught, but....). But in order to get me sponsored by the military, he had to show tax filings for the last 3 years, so file we did.
After he filed, we sat and waited for our expected tax return. Instead we got a letter from the IRS saying 'thank you, we've applied your refund to your outstanding debt and now you only owe $15k'. 
Eventually he came clean and admitted to over $22k in debt. He was - and still is - just freaking useless with money. If the card keeps working, he keeps swiping it and spending. Very recently was told this compulsive behaviour is probably related to the bipolar he's being tested for, but anyhoo.
I was less than thrilled and probably would have walked if we hadn't already got married. Took several years of me working overtime to pay everything off, but we did manage it. That was over a decade ago and now I manage the family finances and control things pretty tightly (he does play along and doesn't 'push it' too often).
I'd say that if he realises he's made a mess and wants to do something about it, then offer your support (not necessarily financial support, though) and see how he goes - does he make an effort, change his habits and pay stuff back etc.