You get to decide what your partner can see in an account you own. To do that, open up that account, tap "Options" and find "Partner can see". That's where you can decide what your partner will see:
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• Share both balances and transactions
• Share balances only
• Nothing at all

You can also decide if your partner can see a particular transaction. If an account has been set to "share both balances and transactions", all of its transactions will be visible to your partner by default. However, if you'd like to hide a specific transaction, say a surprise anniversary gift, open up that transaction, tap "Options", then "Edit Details". After that, find "Visibility" where you will be able to show or hide this transaction from your partner.