Hesitant about Sex

How do you know that your are physically ready to have sex? Because I know that I am mentally ready to do it. But every time my boyfriend and I continue to move forward with our foreplay. I tend to hesitant and stop and then I end up shaking,sweating and looking nervous and we start talking and he can see the look in my eyes. That I want to have sex with him along with the fear in my eyes. Yet I always stop myself. I don't know how to just go through with it. 😔😔😔 sex is a huge deal for me.