MIXED RELATIONSHIP AND HIV
1) unprotected anal intercourse with you as the top (highest risk)
2) unprotected anal sex with him as the top (lower risk , but still risky).
So, you can cum on him during masturbation and he won't get the virus. You can sleep together, and even if your pre-cum dribbles on him, he won't get infected. As for oral sex. it's considered very, very low risk, but you might want to avoid cumming in his mouth to reduce a very, very low risk even further.
You may want to check out some local community organizations for gay men and see if they have any programs for men in couples with discordant (mixed) HIV serostatus. Please have your partner get tested again, if he hasn't already. For more information, call the Center for Disease Control National STD and AIDS hotline at 800-342-2437. It's open 24 hours a day, 7 days a week.
To your health,
HIV testing and care for those who are eligible -- at City Clinic.