PEP is not intended to be used every time you get scared. PEP is generally intended to be used when a person has had a high-risk encounter with someone who is known to be HIV+. PEP can have serious side effects.
When condoms break and expose the head of your penis, it is OBVIOUS. You would not wonder if it happened or not.
When a condom breaks, it breaks completely, from top to bottom. It's not just a minuscule hole. There's no way you wouldn't notice if it had really happened.