He is in a tough spot, because you shouldn't start healing someone of their trauma until the threat is removed, and if he is just lying down, letting the girls take care of him, soothing their worries, some physical threat might come and cancel the effect of the treatment and reaffirm the trauma. Trauma is a part of the body's survival toolkit after all.
He will have to balance between reassuring the girl very slowly and surely, while also looking out for threats. The girls left him alone too many times to actually protect him.
The MC is an airhead though, I think. He spent too much time reaffirming what he assumed to be the case. What he thinks he knows might be correct, but they aren't exactly helpful either. He seemed to miss the implications from the girls that they think his independence is a crack that can allow threats to hurt him. He need to learn more about the reality, particularly about the details of the girls' feelings to actually formulate a plan.
There has to be several unique, active, obsolete traumas from their past that stresses them through their breaking point.
This grim reaper? No, the grim reaper hasn't actually tortured the girls yet.