Every single time you bang, you have a 3% chance for the condom to fail. That means it's a 97% chance it won't. That figure does not change the more you have sex. You just have more chances that you might hit the 3%. Now probability says that that means if you bang 100 times you could get pregnant three times. It probably won't happen like that, because actually that 3% assumes that there is a fault with the condom rather than any user error, so if your condoms are perfect then there is no reason why you would have a problem. There is just a 3% chance that you will. However the real stats for condom use are much worse than that, because human error is introduced into the process and the condom is not used as a perfect barrier.

For comparison, the pill is about 99% effective. This does not mean that women on the pill get pregnant all the time because they have sex over 100 times. It just means that every time there is a 1% risk that the contraception will fail, which is extremely unlikely, and having sex does not make it more likely. However in the case of the pill use error is much less common and less immediately a problem, meaning that there are fewer accidental pregnancies for women on the pill than those only using condoms. That is why even though the stats for perfect use for condoms and the pill look very similar, in reality it is the human element which makes condoms more risky, but if you can manage to use them successfully they will be almost as good.

Basically everyone who is concerned about accidental pregnancy should use two different forms of BC because this massively reduces the risk, since the chances of them both failing at once becomes a tiny fraction of a percent, so basically negligible.