I think the fact that she's gone and everything is going to **** is absolutely freaking him out. He's seems to be on the hinge of going back to his old tendencies (threatening, angry, etc.). He's all alone. In the promo we see Bellamy giving this huge, inspirational speech (which I'm assuming is AFTER that producer's preview clip), and who's beside him? Clarke. I think once she returns he's going to breathe a sigh of relief.