Honesty is the best policy.
While talking about pet peeves such as leaving dishes in the sink or if sharing a towel is acceptable is necessary, finances can make or break a relationship.
If you find yourself in staggering debt or suddenly not well off because of getting fired from a job or a business loss, it is crucial to tell your partner.
Be entirely honest about what happened
If broke is your default status, chances are your partner already knows. But if your business is sinking or you lot your job, you need to tell your partner about it as soon as possible.
Tell your partner before any investment
Should you not be able to tell your partner when you started losing money, make sure the financial situation is known before a major investment that was meant to be joint. Don't sink your partner into a potentially deeper debt.
Be clear about the next plan to take
Are you planning to fix it? If so, how? Ensure your partner is aware.
Make sure to ask for support if you need it
Should you find yourself in a hole, let your partner know if you will need support.
Do it in a neutral location
Such as a restaurant or while out on a walk. Don't confess it during pillow talk or just after giving your partner a gift to "offset the upset".