Condoms are quite dependable for preventing transmission of disease like HIV, but unfortunately nothing is 100%. The tests for HIV are also accurate, but there is always a very small possibility that sometimes a false answer is given. Most likely if you used a condom and had a negative test after 140 days, you are NOT infected with HIV. You can recheck it at 6 months after your exposure to be sure. Most people will have turned positive by then if they are infected. Hope this answers your query. If you have more questions, I would be happy to answer them.