By buddy, I assume you mean an AI NPC companion, and not a person playing co-op. You SHOULD be able to tell him to go to a certain point....bring up gun or binoculars and use the companion action key while pointing at a location on the ground. It may help to have a location that they can land, meaning if you don't leave enough area for them to land they probably will not. If that doesn't work, then take them off your team and choose a different character for a short time, then choose them again and they should come back. Make sure you are just taking them off your active team and not dismissing them from your team permanently if they are not one of the specialists. You also have the option to simply shoot them down with explosive arrows, rocket launcher or guns and then wait out the respawn time to get them back.