James Potter was a fairly straightforward guy. That's why he was so likeable. You got what you saw with him. He was easy-going, funny, good looking. He was perfect. The stress of the impending war is affecting everyone. It's kind of hard to stay calm when you are constantly worried about the next issue of the newspaper bearing the names of the dead, or an attack on the castle. It's even worse on top of preparing for NEWTs. Some people are better at hiding the chinks in their armor than others.