Complex sentence: When they arrive at the checkpoint to Nana's retreat Ivan is upset when he realizes that Ressmore is actually sick and that the real reason she made the trip was so that Nana could heal her.
Split into simpler sentences: When they arrive at the checkpoint to Nana's retreatm Ivan is upset. He realizes that Ressmore is actually sick, and that the real reason she made the trip was so that Nana could heal her.