Withdrawal method odds of success

Okay so I've been dating my boyfriend for 7 months and he's been using the withdrawal method. I'm the first one he has used this with and he was married previously and has two kids who were conceived while using a condom(although we both suspect she was poking holes in them). How many of you have used this method and what was the result? I am scared we will end up pregnant and total we have three kids and his only excuse is we don't have a big enough vehicle for a fourth.