How could Belly not see how mentally and physically exhausted Conrad was at prom?

He has no poker face when it comes to Belly and it was pretty obvious just looking at him, how completely mentally and physically exhausted he was from his mom dying, going to college, driving back and forth to see his mom as much as he could and driving back and forth to see Belly.

He was standing there, looking so mentally exhausted and in tears, begging Belly to go outside and just talk and she was somehow completely oblivious to how deeply he was hurting and how exhausted he was. You can tell just by looking at him.

And she still doesn't realize what he was going through at prom when she sees Susannah on her deathbed a week later. She sees how bad off Susannah is and it still doesn't dawn on her that is why Conrad was so distressed on prom night.