Too many articles about couples and money (but not this one!) talk about how you “must” have identical spending habits. (e.g. a spender will always infuriate a saver, and vice-versa.)
But really, it’s not being the same that’s needed (indeed, it may be counterproductive under certain situations), but rather openness, both in a willingness to talk to each other about difficult topics (money is just one of them), and also in there being no “deep” secrets.
That doesn’t mean you each need to post your transaction ledger on the fridge every month, just that there shouldn’t be any major surprises that affect the both of you. “Honey? What’s this letter from “Educational Debt Collection Services about? I thought you graduated free-and-clear?”, “Sweetie, why did MegaBankCorp just send you a letter about upgrading some PlatinunNiobiumTitanium Exlcusive Deluxe Card I’ve never heard of to a $25,000 limit?”
And, of course, even without skeletons in the closet, you need to be able to discuss money matters and come to an agreement on them. If you agree that you’ll get input for all purchases over $X, no sneaking around trying to hide your new $2X you just had to have. Screwups are frustrating, but coverups make it worse. If you don’t like the rules your partner suggests, suggest new ones…