Why won’t my Apple Pay work for Apple Music?

It sounds like the problem is that your bank did not approve of your card being on your boyfriend's device. When you add the card, Apple sends the bank the details of the owner of the Apple ID, then it is up to the bank to approve any charges made on that card.

You will see here one of the reasons that a payment is not accepted:

• Double-check that your name, billing address, and other information is spelled correctly and matches what you have on file with your financial institution.

Add a payment method to your Apple ID - Apple Support