My partner doesn't have a job or credit card, so I opened an account for him to use.

Why is this against the TOS? He's the only one that uses it. Nobody else.

Can a blue explain.

If you wish to pay for your partner's then it should be registered in their name, and thus make them the registered user. If, however, the account is registered in your name then you are the registered user and sharing the account outside of the specific situations outlined in the Terms of Use (http://www.worldofwarcraft.com/legal/termsofuse.html) would indeed be a violation and should be avoided:

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Q u o t e:
3. Establishing an Account.
. . .

During the registration process, you will be required to select a username and a password that are unique to the Account (collectively referred to hereunder as "Login Information"). You may not share the Account or the Login Information with anyone other than as expressly set forth herein.

. . .

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