Intentional or negligent transmission of HIV is classified as bodily injury according to German law and is therefore punishable.
Whether a punishment is actually imposed, however, depends upon whether or not the HIV-negative person knew about their partner’s HIV infection and consented to unprotected sex.
Those who do everything they can to protect their partner, by using condoms for instance, are on the safe side criminally speaking in any case.
If the partners mutually decide to stop using condoms in the relationship, the agreement should be made or documented in the presence of witnesses.
Whether a viral load below the detection limit offers sufficient protection for the partner is a question that is answered in a wide variety of ways in the German courts.
You are not obligated to inform sexual partners of your HIV infection in Germany.