Am I Being Unreasonable? Original Owner Wants Car Back

It's your car and you can simply say "it's not for sale at this time". Also, it's your car and you can name the price that you would sell it for. You are not obligated to him or his attachment. It is nice of you to consider his feelings, I might do the same. But not obligated. You are not even obligated to "give him first chance" if you were to put it up for sale. I know, it's the nice thing to do. In the end, it's your car, you like it, you set the rules and boundaries and he has to live by them. Best wishes to both of you :)