My bf sed tht im too friged and says if i dont get off with him he will split up with me what shall i do? plzz?

Well i have a bf called josh and he sed to me tht im too friged and stiff but i really like him and he said to me the onlii waay he will sty with me is to gett off wid him buh im really nervous because i have never done it b4 wht shall i do ? :'( plzz helpp me asap !!!!