I will be doing trail riding, possibly showing, and endurance racing with him. I wouldn't be able to do ANY of those things if he was a stallion, because most shows won't allow stallions to be present, trail riding would be unsafe because of the possibility of meeting a mare in heat on the trail, and endurance riding for the same reasons. Plus, what reason do I have to keep him intact? He is of very good breeding, has a great temperament, and is registered, but many many horses have those things. I don't have the set up for a stallion, I plan on getting a mare some day (which would not work if I had a stallion!), and I have no plans of breeding.
Also, gelding is not a huge deal when they that young. The vet puts them to sleep, does the deed, then the colt gets up with no idea of what just happened. He is sore and stiff for a while, but he gets over it quickly and never looks back.
Talk to your boyfriend and tell him that if he wants your horse to be as happy as possible, have him gelded. A stallion that is not allowed to breed and is in solitary confinement is not a happy horse! Gelding is MUCH better for your horse's happiness in the long run.