help please

any tips on fingering and/or eating out? my boyfriend(who is trans) says i do it good but then he says things like you could practice and i don't even remember what else but i wanna be good at it and get him off. my main problem is that i don't do it long enough but my hand gets numb and hurts after doing it alittle while. i don't know what to do😭 i just need help and next time i see him i wanna blow his mind away. please help