Your history is incomplete. You were HIV
some 6 months ago and you had exposure some 18 months back , so in all practicality you have crossed (18-6=12 months) the maximum 'window period' which is 6 months
Considering that your condom even did tear, during your activity, you stand negligible chance of getting HIV , as you tested negative even after 1 year of exposure , which is double the window period of HIV.
Window period means here that HIV virus may remain in the body of a person , but HIV may not produce enough antibodies
to be picked up by standard HIV tests and may take max 6 months to make enough antibodies to be picked up by standard tests of HIV to render it a positive test .
Hope this does help.
Dr Matin .A. Khan
MBBS, MPH, MMSc (HIV Med) PhD
M.A (Sociology) , M.Sc(Psychology), M.Sc(Counselling
Fellowship in HIV Medicine (School of Tropical Medicine Kolkata, India)
AAHIVS ( American Academy of HIV Medicine USA)
Galen Exam for Certificate of Clinical Competence in HIV Medicine from IAPAC USA
MGM Medical College , Jamshedpur , India