How can I do my boyfriends taxes on here if I've already done mine on here

account and user ID.   If you use the same account and user ID for a second return, you overwrite the first one and lose it forever.

When you use Desktop TurboTax, which you install from a CD or download to your own hard drive, you can prepare and e-file multiple returns for the cost of the software.  You can e-file up to 5 Federal returns—more if you mail the additional ones.  If you have multiple returns to prepare for family members, Desktop is more cost effective.

Desktop --unless you specifically buy federal  Deluxe only from a retailer-- will include the software for one specific state.   You can prepare as many returns for that state as the number of federal returns you prepare.  E-filing state returns is an extra fee which can be avoided by printing and mailing the states.   Additional--other--state software is an additional fee for the software.

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-online/00/25596

https://ttlc.intuit.com/questions/1901306-how-many-times-can-i-e-file-using-the-turbotax-cd-or-download

https://ttlc.intuit.com/questions/2750704-what-are-the-advantages-of-the-turbotax-cd-download-software-over-the-online-version