I Do Because She Won't

Of all the many fetishes and kinks that my wife and I share between us you'd think that there's almost nothing we won't do, however we share one aversion, neither one of us likes to tongue a man's ass.
I can spend all day licking my wife's ass or any other woman if I am lucky enough to get the opportunity. Even my wife, on the rare occasions that she's played with another woman, has licked female ass without hesitation.
I'll suck and lick her from her head to her toes. I'll lick his cum from anywhere on her body. I'll suck his cock and swallow his cum if my wife allows him to cum in me.
But we both share the same aversion to licking men's asses.
That being said, she has a semi-regular lover named Bill. Bill is a salesman and only passes through here a couple of times a year. She really likes him. She has told me that he is a fantastic lover and a fun date. I actually like him too, a very nice guy who understood and came to enjoy our lifestyle very much. Sometimes I got the feeling that he liked to visit "Kaaren" as much as he liked to visit my wife and I was almost always included in their lovemaking in some way.
Bill had a fetish too apparently, he liked to have his asshole licked. My wife turned him down repeatedly and so did I.
Finally one night while we were waiting for him to arrive my wife sheepishly asked me if I would do this for him. She said that he would be so happy and that she would really like to make this happen for him. She said she would understand if I declined but she would love to make his last trip our way this year memorable for all of us.
She looked me in the eyes and I melted as I always do. There is nothing I wouldn't do for her and she knows it.
When he arrived he kissed us both and he and my wife snuggled for a while. She worked his pants off and slipped down to take his cock in her mouth. She beckoned me with her fingers to come closer and as she pulled his legs up I stuck my tongue in his ass and began licking.
It wasn't really so bad, no different really from licking my wife except for the view. It's probably just a psychological block or something but as his hand pulled me closer and he moaned my name I really began to work him in earnest. I could tell from the look in my wife's eyes that she was very pleased with me and that only made me work harder.
When he came he nearly drowned us both. I have rarely seen a man who looked happier or more satisfied. I was glad I was able to make them both so happy.