Did you ask your boyfriend about his finances directly? If not, I’d start there, if you’re pretty serious already. No point snooping around.
If you did ask….and you’ve been in this relationship for something longer than a few months(to the point is pseudo serious now), apparently, he “forgot” to file a 10-k disclosure to you from the time you folks started dating until now, and there isn’t any reason why you should have to pick up the excess baggage.
If you really love him and plan on marriage, get him to sign a prenuptial and make sure you keep separate accounts temporarily.
Then make sure you tell him you’ve decided to assume the CFO position in your household with at least 50% controlling stake and that he has a remaining 49% stake and that the remaining 1% is left to a coin toss which he can optionally exercise at most 2 times per year on expenses $5k or less, because obviously he did a piss poor job in the past.
Also make sure in the contract, that it clearly states unauthorized purchases without the explicit consent of the CFO will result in automatic disciplinary action, which includes no sex, no football, no beer for 3 months. And second offense results in above said disciplinary action for 6 months.
If he doesn’t agree, time to find another boyfriend without so much baggage.