Anal...good or bad?

My boyfriend really wants to do anal, and I’m definitely open to it because when we have sex he will finger my butt, and it feels great. But he is big down there so i thought maybe we should buy butt plus to kinda size up. Well one night it just kinda slipped in and it hurt so bad i kicked him off of me balling my eyes out. I still wanna try and do anal tho, but how?! How do i try and relax??? I wanna be so pleasurable for him