Salutations baigou,
It sounds like you’re sharing an iCloud account with someone by both you using the same Apple ID. Otherwise, Family Sharing would allow you to each use your own Apple ID but still share the iCloud storage.
if you’re both signed in on a device with the same Apple ID, you both have access to the same data whether this be Apple Pay, Contacts, iCloud storage, etc. There isn’t a way to restrict the payment method added to that Apple ID, other than to remove the payment method. However, a payment method is required on the account if there are any active subscriptions.
If your goal is to share the iCloud storage, then using Family Sharing is the best option. Here’s an article with more information on what Family Sharing is and how it can benefit you and the person you’re sharing with - What is Family Sharing?
Thanks.