He might look happy, but only she knew how insecure he was about her safety. He didn’t dare to spend much time in the shower as if Kate would vanish from his life the moment he comes back to his sense from his dream, 

Yeah, a dream, sometimes David feels like everything is a dream, making him panic. Sometimes in sleep, he cries and calls Kate’s name or wife. Kate experienced everything and saw his miserable state, but she didn’t dare to confront him.