Is there possibility of not contacting HIV after sleeping with a HIV person unprotected? Yes

A HIV person person can have unprotected $3x with a HIV negative person without infesting his/her.

This however depends on some empirical factors which comprises:

The viral load of the HIV positive person, Use of PreEP (pre-Exposure Prophylaxis) by uninfected party

Anti Retroviral Therapy or ART is medication designed to limit HIV from damaging its human host immune system by retarding its multiplication in the host.

ART requires six months to start working in the body of a person living with HIV. In some cases, consistent and timely use of ART by a person living with HIV can drastically reduce the viral load of HIV in a person body into an undetectable level; when this happens, the person is said to have attained: undetectable viral load.

This implies that the person is incapable of infesting any with HIV through $3x.

However, this is risky as a person with undetectable viral load of HIV can get infected with another strain of HIV through $3x.

Pr-Ex Prophylaxis is a preventative medication that disallows HIV from taking hold in one’s body.

This is intended for people who consider their partners high risk of getting infested by them.
Pre-Ex requires seven days after administration to start working and is capable of reducing chance of contracting HIV to 99%