How come Simba did'nt want Nala to be around when he was talking to Kiara just before the song We Are One.

What makes Ты think it was about what Simba wanted? To me that moment seemed like Nala herslf decided to leave Simba and Kiara alone because Simba needed to be the one to talk to Kiara because it was his order Kiara had disobeyed and he who was supposed to raise Kiara into a responsible Queen and all. If anything, Simba seems in that moment like he really doesn't want to do it and would gladly leave it all for Nala to take care of.