what should i do when my girlfriend always ask me for sex but i am not ready

I believe that pre-martial sex is a no-no.Buy she have always bugged me to have sex with her.I have always believed in god and have wore a chasity ring to promise that i will not have sex before marriage.what should i do?anyone pls help me as i am afraid my girlfriend will leave me.Her attitude is very good during normal times but when she keep pestering me,my mind seems to think whether i should have sex with her.