Brian felt torn as they made their way through the forest towards town. He knew Mike was being foolish, and that just going back to the stable was dangerous enough. Mounting the mares would likely make him a horse again, and Tye was not going to keep bailing the centaur out of trouble. The stable boy mindset was telling him that if the transformation was done right, not even Tye would be able to change Mike back to a centaur.
Worse, Brian was having more trouble resisting the urges to do everything he could to turn the useless centaur into a valuable work animal. No, not useless! Mike was a fighter, a member of the party. Then again, he had no real experience or training in fighting, and he seemed to be taking every opportunity to get himself changed into a draft horse. Brian had to admit he was helping a little there - the centaur was seeking out mares largely because his sexual needs had been amplified threefold or more. The stable boy identity had brought more than the body and mindset - Brian had discovered that he had some limited magic that let him control and transform equines. Not instantly, like Tye or the wizard, but given time he could accomplish just as much.
His fingers had been working while they traveled, grooming Mike's mane. He could see that it was longer and thicker, and that horse hide now extended from it halfway across Mike's human back. Seeing the change gave Brian a thrill. He imagined stroking Mike's face, drawing he ugly, flat features into the muzzle of a great Shire. The thought had him shiver, ad he realized he was erect, his cock rubbing hard against the ridge of mane that started at the base of Mike's human back. A benefit of being naked. Brian savored the sensation, appreciating his new body and abilities. Why was he even considering joining the party on this adventure? Working as the stable boy gave him adventure, excitement, pleasure, all without much risk. Not to mention the intense sense of power when he used his magic on Mike. Brian realized that he really liked everything about being the stable boy, enough that he really didn't want to go on the adventure. In fact, he did not want to go back to his own reality.
They reached the outskirts of Lavenguard, and Mike made his way quietly as possible through the quiet streets. Brian grinned to himself as the centaur took them to the stable and pulled the doors open enough to enter. Mike was making this all too easy. And if his friend wanted to join the animal kingdom, Brian was all too happy to help. He was the stable boy, after all.