I know you would like to help your boyfriend with his credit by adding him to your card or signing up for a joint card. However, I strongly suggest you do not do that.
First off, authorized user accounts have been targeted and are being phased out from the FICO scoring system. Therefore, your history will not help him in the long run.
Secondly, even though you and your boyfriend are on great terms now, what will happen in the future if you share a joint account. Can you be guaranteed that he will use the credit card wisely? No one can make any guarantees. If he forgets to make an on-time payment, put the credit card over the limit, or completely runs amuck with the card, IT WILL DESTROY YOUR HARD EARNED CREDIT - EVEN IF IT IS ONE 30 LATE WHICH CAN REDUCE YOUR SCORE SIGNIFICANTLY.
The best thing for you to do would be have your boyfriend open a secured credit card account with Orchard Bank. This is a great card and has helped many in your boyfriend's situation. If he uses it wisely, it will build his credit as it reports to all the major credit bureaus. Also, this will protect you. Also, by introducing him to a forum like this and helping him learn about credit without risking your own, he will be able to put himself on solid ground. That will be the best way to help him out.
Good luck and please keep us posted.
