While it is true that if he pees in between it lowers the chances, it doesn't mean you shouldn't worry. I know the pull out method is a lot better then just letting him do it inside you, but you really should be more careful. It just takes one time of him not pulling out soon enough. Even if he does pull out every time early, you may end up pregnant. If you're not looking to get pregnant, I suggest using a condom EVERY time. If you don't want that, then talk to your mother about getting you on birth control. You can make up another excuse for why you want to be on it, but you really should be on the pill when you start to have sex.
in your case its a much higher percentage
The more times you use this method in one night the higher the chances, especially if you are ovulate. I've never heard of peeing preventing pre-ejaculate, it's all very risky. I am the type of person that only needs looking at to get pregnant though..still if you don't want a baby then this method is not enough!
Your chances of getting pregnant in a given menstrual cycle are said to be about 20% when you have unprotected sex, and having sex several times in a row with him coming in between (but not peeing or having time in between) is as good as unprotected. Google "Cowper's Gland" if you want an explanation of the pre-ejaculatory fluid and why it can have sperm in it in the next erection after ejaculation.