I stumbled on your post and had to stop. I love, love, love fisting. High-quality lube is essential. Patience on his part is also key - and if he is the pro you say he is, he already knows this. Try playing with your clit as he is working his fingers/hand into you. Your arousal will multiply as you work the clit and you should open more easily to him. A word of caution, however.....once he's in and you orgasm, your cunt will most likely clamp down on his fist and you'll have to be just as patient for the muscles to relax for him to withdraw. During one such session, my partner was trapped inside me for a good 30 minutes....something I didn't mind much at all - lol!

Have fun!