<human>: My live in BF of four years has always made comments and hints towards his preference for anal sex. We've done it a few times in our many years together, though it always is very painful for me (no matter what kind of lube we use, etc.). After we have anal, I can hardly sit for a few days following. I made it clear to him that this painful for me, and he says he cares, and always asks if he should stop, but then just continues going through the motions, and it makes him come very fast. 

I don't understand why this is such a turn on for him, especially seeing as it so not pleasurable for me. I agree to it every now and then because I want to make him happy and because I am afraid that if I don't give it to him, he'll seek it elsewhere for all I know, as he mentions it a lot (wanting to have anal). 

Should I continue giving in and deal with the pain during and following or should I just say no? Can anyone explain to me why the strong preference for anal over vaginal? 

I feel torn between making my BF happy and satisfied and putting up with the [I guess brief?] pain.

Can you condense the text into a few key points?
<bot>: BF prefers anal sex, even though it's really painful for me. Should I keep giving in out of fear that he will remain unsatisfied and leave me, or just refuse?