Condom True Effectiveness?

Caitlin
I have the house to myself tomorrow night, so I'm having a guy over. There's a 90% chance, we're going to have sex. This is the first time I will be having sex since coming off the pill in early May. How effective are condoms for real though? I know they are effective, but I'm kinda nervous about it. Has anyone else ever been paranoid about relying on condoms?