How do i take this? what if he lies and tells everyone different?

Ok , so me and this guy have known each other for a really long time and last monday , he broke up with his girlfriend and said he loved me , and he needed me in his life and that i was the only thing that made him happy .so we started dating, yesterday we have been dating a week, And we meet in church, our parents have been friends a long time, and they know pretty much everybody in our family, and we would see each other a couple of times outta church , but it was when our parents where together , so nothing happened, and now that we have been dating he went from , sweet chirstan guy, to a nasty perv only wanting sex. and now its only been a week and hes telling me hes "in love with me " and he "wants to sleep with me " , and is always teliing me this , and its like all he wants is sex, and im really not ready for that , but how do i tell him no? , everybody knows that we are dating , and i have no way out of this , because if i tell him no , hes gonna get mad, and we are going to end up breaking up, and everybodys gonna know and ask what happened , or i go with it and have sex with a guy , that i dont want to . not ready for . ..... what should i do ??????