To sell or not to sell

So I have "pony" (small horse) Griffion that I have been leasing out for the past 5 years. Now that he is coming back to work I am wondering if I should sell him or send him out on a contracted lease.... I cannot seem to figure out what the best option is. I have had him now for about 10 years and he was my first horse. It was be very hard to part with him.

 Another reason I would struggle is because he was abused. His first owner beat the crap out of him! When I first got him he would not pee in his stall. He would hold it all night until turnout and wouldn't even make it out to the paddock and have to stop and pee on the way there. Someone told me his last owner would beat her horses if they peed in their stalls. The reason being is she didn't like to clean pee out of the stalls. I tried to lunge him when I got him he just ripped the line out of my hand and ran away. It was evident he had been beaten with the lunge whip. I rode him with a small crop and when I went to tap him because he was going a little slow (I was 11 at the time) he bolted and dragged me against the fence and dumped me on the ground. That is when I knew this horse needed some work. He needed to trust humans again. I slowly worked with him like you would a foal. Touch him all over and dragging a whip along his back. Using slow movements. Eventually he became trusting of me but still showed signs of anxiety. As the year went on he got more and more comfortable with his life. His personality came back and he was a cheeky pony. He no longer fears whips or loud noises or anything for that matter. He has done, barrel racing, jumpers, hunters, trail riding, cross country, dressage, Prince Phillip Games, drill team, lesson horse and fox hunting. He would be perfect for an older amateur or a younger kid who wanted to do dressage or some western stuff. I would really have a very hard time parting with him tho due to our history.

I would love to lease him out on a longterm lease contract 2 or 3 or 4 or even 5 years. I think that I will have to keep 'my little pony' forever because there is just something about him.

Have any of you ever had a hard time parting with that special horse or pony? What was the best option for you?