It sounds like the player isn't 'clicking' with the harsher system. I had a similar thing happen with one of my players when we moved from D&D to Only War (a Warhammer 40K based d100 system where you're often rubbish at everything). He failed a lot and would sulk as a result. We explained to him that this is how the game works and he decided he didn't like the game and sat this campaign out. We have a group where people come and go so this wasn't an issue, though I don't know how suitable it is for your group.