I'm sorry to hear that about your boyfriend. If she was aware that she was HIV positive and did not disclose that information then she committed a crime and should be held responsible for it.
Unfortunately, precum is considered a body fluid and can contain concentrations of HIV.
Here is some information from CDC.gov:
How is HIV passed from one person to another?
HIV can be detected in several fluids and tissue of a person living with HIV. It is important to understand however, that finding a small amount of HIV in a body fluid or tissue does not mean that HIV is transmitted by that body fluid or tissue. Only specific fluids (blood, semen, vaginal secretions, and breast milk) from an HIV-infected person can transmit HIV. These specific fluids must come in contact with a mucous membrane or damaged tissue or be directly injected into the blood-stream (from a needle or syringe) for transmission to possibly occur.
In the United States, HIV is most commonly transmitted through specific sexual behaviors (anal or vaginal sex) or sharing needles with an infected person. It is less common for HIV to be transmitted through oral sex or for an HIV-infected woman to pass the virus to her baby before or during childbirth or after birth through breastfeeding or by prechewing food for her infant. In the United States, it is also possible to acquire HIV through exposure to infected blood, transfusions of infected blood, blood products, or organ transplantation, though this risk is extremely remote due to rigorous testing of the U.S. blood supply and donated organs.
Which body fluids transmit HIV?
These body fluids have been shown to contain high concentrations of HIV:
other body fluids containing blood
The following are additional body fluids that may transmit the virus that health care workers may come into contact with:
fluid surrounding the brain and the spinal cord
fluid surrounding bone joints
fluid surrounding an unborn baby
Although it is less common to get HIV through oral sex, it is possible and your health should always remain a priority. Please use protection always and continue to get tested throughout your relationship.
Wishing you the best,