I think it's the right behavior he should be having in front of maki. The person is already in distress, having your significant other in the same state may harm him even more...
Shuu-Chan needs to be the calmness that makes Mai-Chan calm. If Shuu-Chan is freaking out & going crazy it would distress Maki more. Maki needs a solid rock to lean on right now.
I don't get why shuu chan is so calm? I feel so bad for Maki I can't even describe how angry I am right now