Any fuck that gets him off is a good fuck. Her feelings, comfort, pain are irrelevant. We are just a set of holes put together for the purpose of satisfying a cock any way any man wants it.
If a friend/cuck offers you their wife/gf you make sure to destroy her and him when you do it. Destroy her pussy and image of her forever while also destroying his dignity. That's what cuckolding is truly about. Tell him you'll take it easy but pound her holes as hard as you can instead.