So I have an Appendix horse and he's 10 I'm 297 lbs,will I hurt him if I ride him?

The rule of thumb is that the rider should weigh no more than 20% of the horse's weight. So, if you weigh 297 lbs, the horse would need to weigh 1485 lbs. If the rider weighs more than 20%, it causes stress to the joints, muscles, and bones of the horse's back and legs. You can buy a weight tape at most any tack store or feed store that sells horse items.