don't feel bad, you know they enter our lives for a reason and you know he will have always taught you something. Sometimes the first one just isnt the perfect one, just like dating. I had my first horse for 4 yrs and I did all kind of training for her and to her and we just didnt get along but she was a good girl, I ended up selling her to a really nice 15y/o girl too and they did amazing. But it put me in to place to find the "one" and I did and so it was a good thing. But I will never forget my mare and everything she taught me. So don't be sad be happy he's going to a great home and that you had the time you did with him and what you've learned from him.
"The horse you get off is not the same as the horse you got on; it is your job as a rider to ensure that as often as possible the change is for the better."