Good on you for putting your horse's happiness over your personal ambitions. There are a lot of people out there who don't, and they battle along with a horse that isn't interested in or enjoying the work. Horse riding is supposed to be FUN. If you aren't enjoying it, your horse probably isn't either. While it's normal to hit bumps in training where you have to push the horse through, there's a difference between a bump and a brick wall. If it's causing you and the horse no end of stress, then it's perfectly reasonable to reassess whether the horse is suitable for the job. It's much easier working with a willing partner than one who fights you every step of the way. Where is the joy in that? You're lucky that you've discovered a new passion that your horse will actually enjoy. Usually you have to get a new horse when you switch disciplines, and selling your current horse can be heartbreaking. I recently returned to dressage after focusing on endurance for a few years, and selling the mare I bred for my endurance dreams was soul shattering. The silver lining is she has gone to a fabulous new home and is thoroughly enjoying her endurance career, so I don't feel the least bit guilty for selling her. She would've been miserable doing dressage, and realistically there's only so far you can go in dressage with an Ay-rab. Your horse is still young with plenty of riding years left in him. You will have a blast in your new discipline, and both be happier for it. And you can still go for trail rides and camping trips if you start missing the trails! Sometimes quitting is the right thing to do and it's always good to reassess your goals every year or so to make sure it's what you still want.