What does it mean when a man suddenly becomes icy and reluctant to talk after

[desertrose11]

getting a long so well? I'm a teacher and one of my little girls' father got a long with me very well. We would talk a lot and he was always very friendly, yes occasionally the slight flirtation. All of au sdden, he stares pretty intensely then looks away. Or when I smile he doesn't really smile back. He will talk to me, but I can feel this mild tension and reluctance. It feels odd professionally so I'd really like to have an idea of whats happened. Its confusing, help!!