He wants to ejaculate inside me 😳

So my boyfriend has been wanting to finish inside me at least once. I told him I would let him bt then I thought there is a 50/50 chance I could get pregnant if he does it just once. I dont plan on having kids for at least 8years from now. I want him to do it cz the odds are I don't get pregnant if he only ejaculates inside me once.  Bt I am scared to get pregnant 😝