It is difficult to give a number or percentage to the chances of getting HIV, because there are many factors that could come into play. There are things that can increase the chances such as a high amount of virus (viral load) in the blood, or having another STI at the same time. Likewise there are things that can lower the chances such as condom use or low viral load.
Condoms provide excellent protection against HIV if, as you note, they are used properly and they do not break or fall off. In your case it sounds like you are doing that, so your chances of getting HIV should be very low.
Look here for more info on proper condom use.
Please leave a comment to let us know if this answers your question or if you need more info.