You could do a free lease on him if you aren't sure of actually selling him. If you find after he leaves, & is gone for a few months, that you can deal with him being gone-- you could sell him then. A free lease is a good way to let someone have the pleasure of having a horse but you still own the horse. I understand what you're going through here- I have a 9 year old Thoroughbred gelding who is by far my favorite horse because he's the same horse everytime you ride him-- but I have a green broke stallion, a VERY nervous/scared 8 year old barrel racing Quarter Horse, and a real brat of a off track Thoroughbred mare who are getting my attention more than my best gelding. As long as he isn't being neglected(as in starved, never talked too/brushed, etc) I'm sure he isn't minding just being a lazy pasture ornament.
Sit tall in the saddle, hold your head up high, keep your eyes fixed where the trail meets the sky, & live like you aint afraid to die, & don't be scared, just enjoy your ride.