Question

I know it's pretty much impossible to get pregnant unless a penis enters a vagina and gives those little sperm a six inch head start. But....Is it possible to get pregnant if there's sperm on a toilet seat?

I'm a virgin and it's my first time living with roommates. My one roommate has sex with her boyfriend at the house once a week. I'm paranoid that he will go to the bathroom and take off his condom and pee and that somehow I'll come in contact with his sperm if I use the bathroom next. Can someone who has experience please set my mind at ease without calling me a troll or something? I need a reassuring message.