Maybe you can lease your horse out to this person, so that if circumstances change in the future you can get your horse back, or if they keep going forward as you plan then in the future you could still sell. Just a thought, I think either way will work out for you.
I had my first horse until I was 22 when he passed away. I was training horses at the time, saving money living at home with my parents. I was ready to move out though, and had just met my boyfriend. We knew we would get along and that it would be a good thing, but for most of the beginning of our relationship I was without a horse, but still around them all day.
I let a few years go by, training horses, going to school, still making a little income, until I had finally saved $5,000. I started looking for another horse. I found Dodge, who needed me, probably more than I needed him, but it was a good thing. I knew I would start my career and I could afford the horse for 6 months while I finished school.
I accepted a job, moved, started work, and a month in a horse I had trained was offered to me for free. I took him, now living in an apartment in one of the most costly places in the world (SF bay area), with 2 horses and a jobless boyfriend.
For the past 9 months I've been paying for rent, groceries, and more for me and my boyfriend, and my 2 horses. I don't make a lot of income, less than average for the state, but enough that I can still save some, and I'm about half way to a decent down payment for a house. I also manage my money to the dime, sometimes the penny...
This works for me. Plan your income, expenses, see if you can do both, have a horse and save for your future. If you can't afford both, it may be better to skip horses for a couple years in order to afford them for a life time.