Anal Sex 🙈

My SO and I have tried Anal before but it never really works out (he has a big penis) ! A few different times he's got it in but I give up cause it hurts and feels as I'm going to relieve myself all over him Lol! I just want to know is there any techniques I can use to get use to both feelings? I want to give him the pleasure of being able to pick and choose which hole he wants 👅.