Have you ever wondered if SS really misses his home? About those whom he lost? He is so lonely that he begins to talk to himself.
It seems to me that without his brothers, it is very difficult for him. And everywhere, even in shooting stars, he sees their sparks.
I love how in Tfone Megatron beat the shit out of Starscream in front of his whole army and not even a day later Starscream and the others were willing to die for him.