His Wife, My Fuck Partner

These past eleven weeks I've been sharing my best friends wife.
He got injured during a football game and wasn't able to satisfy his wife.
She's an extremely sexual woman who wants and needs cock every day. He couldn't give her what she so desperately wanted with his injury, so he asked me if I'd consider fucking her.
The thing is, he said it right there in front of her.
Michelle isn't the best looking woman, but she honestly is a complete nymphomaniac as I've found out.
The evening he asked me, Michelle and I did just about everything together sexually, from kissing to her rimming my arsehole as I finger fucked her pussy and rear hole at the same time. And as for fucking her, she literally wore me out.
We spent the last half an hour of two hours of sex, with my mouth clamped to her clitoris and her having one orgasm after another.
And during the whole two hours, my best friend watched and encouraged me as he masturbated.
The following night she turned up at my place and we fucked all over my flat.
And that's how it's been for eleven weeks. Sometimes I fuck her in front of my friend, other times she'll stay over and we'll fuck all night.
Usually we get together at least three times a week, but it can be as many as five times.
My friend is almost back to full health, but he's recently told me he'd like me to carry on fucking Michelle as it "Helps him out".
And I fully understand why. His wife requires more than one man to keep her sexually happy. And if they both want me to continue fucking Michelle, I'm going to carry on enjoying her dirty bitch ways