Hello and welcome to e health forum.
The chances of you being infected with HIV is very less likely, as you had a intercourse with your girlfriend, who might not be infected in the first place.
In addition , since your tests have been negative since the last 5 months, you need not worry about HIV.
Using a new blade , for shaving does not lead to HIV infection.
In addition, Once HIV is outside the human body, it loses its infectivity within a few minutes (5min - 20 mins).