I have been thinking about this a lot recently and though its far fetched there may be some truth to it. What if Kylo Ren, aka Ben Solo has not fallen to the dark side but instead is working against Snoke and the First order. We know that Snoke had been watching Ben Solo for years waiting for him become a competent force user and having him turn to the dark side. What if Ben saw Snoke’s power and came to believe that the only way to defeat Snoke was to gain as much knowledge and power from him as possible and then destroy him once and for all. Maybe Kylo has fallen down a dark path but for the right reason, after all when he encountered his father he said:
I’m being torn apart. I want to be free of this pain. I know what I have to do but I don’t know if I have the strength to do it. Will you help me?
This would be the ultimate sacrifice to prove to Snoke that he is ready for further training. Maybe he let go of the Ben identity because Ben was too weak to defeat Snoke and thats why he became Kylo Ren:
Your son is gone. He was weak and foolish like his father, so I destroyed him.
This would explain why he wanted to Keep Rey alive, he saw her as a powerful ally someone that could help him stand against Snoke, as opposed to the Resistance or as he stated:
Do you mean the murderers, traitors and thieves you call friends? You’ll be relieved to hear I have no idea.
We know Luke is the last Jedi so maybe Kylo/Ben and Rey are the beginnings of a new order or force users who are more open than either Sith or Jedi. After all the Jedi close themselves off from temptation to stave off the Dark Side, but against an entity like Snoke abstinence may not be effective. It may be a little bit stupid but its possible that Kylo heard Snokes call and recognized it for what it was and was disgusted with Luke’s ability to deal with it and decided that the needs of the many out weighted the needs of the few. I am well aware I just quoted Star Trek and that I am comparing Kylo to Itachi Uchiha but this is all plausible.
When a police officer who worked undercover in Narcotics was asked about the effects of going deep undercover he has this to say:
What might appear as innocuous fantasy or role-playing, when conducted under stressful or life-and-death situations exacts a heavy toll on the individual forced to slide in and out of character.
This could help explain Kylo’s extreme mood shifts, one of the best examples is when he destroyed a console for no reason other than anger.
This could be another reason he wears the mask, though apparently it is a Sith Mask, but it helps hide is true emotions. Ben could be buried under Kylo just waiting to come out.