Oh God Its Painful His Cock Is Too Big For My Tight Asshole

My boyfriend really loves getting me from behind but, lately his sexual desires turned him towards anal, I really do not like it, because his Mandingo cock is simply too big to fit inside my tight little asshole. I want to please him and he is all i got but my butt is not big so it feels a bit odd. What can I do, in this clip you will se the way that he likes it any ideas?