Yes OP, you should get the horse some help. You could buy it from Ethan before he kills it outright. You might be able to get AC on it if there is a current wound that seems aged, ie has pus or mangled flesh or partially healed noseband stripes.
I’m not going to say your story is made up. I beat myself up with regularity for not paying a call on someone, someone whose horse was a LOT thinner than she had made out to be. That horse died during our rough winter, and if I’d been nosier and pushier it might not have. Instead I happily gave advice that was never taken and wasn’t really appropriate for a horse that had gotten that thin anyway.
OP I’d really think twice about that fiancé of yours if this sort of thing doesn’t bother him because it’s “his buddy”. Some buddies are worthless POS.
[And I see that your fiancé didn’t want to buy the horse for you because it’s cut up worse than he thought. My my.]
I can see how you’d be loading up your horse at the trailhead and in comes Ethan but you have to go now so you ask your fiancé and he’s driving and not about to stop and you hear about part of it later, that Ethan didn’t fall off and the horse run off, instead he made a choice, and still later get the rest of it. What KIND of choice he made.
I understand that if you thought it would be collected the next day you’d not go hunting for it, maybe you have kids and a job and all that. Maybe you don’t have your own car or know the trails where the horse might have been left. Maybe Ethan’s one that “needs shooting” a mean type fellow and scary in his own right.
I’d say that the next step for the horse on Ethan’s part is to up and shoot it when it doesn’t do what he wants yet again. He might auction it straight to the KB also, but if he’s a mean sort that won’t give him the satisfaction of showing it who is boss.
That is NOT the sort of person I would want as a friend, or my DH to have as a friend.
AC varies from county to county and state to state. Generally you can make an anonymous complaint in which case you need photographs of the abuse, ie the noseband and the wounds. It has to be something that a judge would see and say is cruel. Stories , even if they are horrific, aren’t too good without eye-witness corroboration or photographs - good sharp clear photographs. Maybe the judge will remove the particular horse. Maybe there are others treated roughly in that manner. If AC doesn’t act then taking the story to the local news outlets can be useful. Best of luck to the poor horse.