Well maybe he can join in with Echo and rail against Orion, trying to argue how the Imperium isn't all that bad and try to convince the group to not give way to heresy. His loyalty to the Imperium and trusting of his comrades would be conflicting, especially since he is so young, so I think he would try to convince Soin and Karliel to not abandon the Imperial cause. He may quote the Lectitio Divinitatus and argue against what Karliel has said and argue that this whole debacle on this planet was due to Chaos and heretics by using both naive arguments he grew up with and what he's been taught during his training for the IG.
But also, because he is so young, its possible his views might have changed during his experience so far since he hasn't exactly seen much of the world and has been dealing with this rebellion for a while, especially his formative years as a young man in the Imperial Guard. He saw how an Astartes failed where his own group had won (the image Orion showed us), he saw how mutants were given the prize that he and his group fought for, and he also saw how Orion was fairly merciful to the group and instrumental to saving the planet whereas the Imperial side only sent a group of mercenaries to recover narcotics and to not help bring the planet back into compliane. Because he has grown somewhat attached to his comrades and seeing how they are all veterans of one sort or another, it might convince him to join their ranks in apostasy seeing how they were so willing to do so and how the Imperial presence was lacking on the planet that was rife with chaos and bloodshed.
There could be completely others ways to look at it but those are the two main ways I see him reacting according to how you described his emotions. I hope that helped! :D