Pregnancy possibilities?? help please

So recently my boyfriend & I have been having unprotected sex. Not the smartest, I know. And I'm not in birth control..
He pulls out every time with enough time
Not like he's literally busting as soon as he comes out but he pulls out and after coaxing a couple seconds, finishes. 
But I'm worried that even though he catches it early if there's any way I could get pregnant. Like this seems like a stupid question & the answer will always be yes, there's a possibility, but I mean does anybody have like solid factual evidence/background support? That there's something that might jeopardize that that happens right before cm even though he pulls out? etc