Starscream is disillusioned by his leader Megatron. It took a while for Starscream to come to grips with Megatron's faults, but there's no turning back. Megatron doesn't respect him, doesn't appreciate him, and would casually toss Starscream's life away if it got him something he wanted. If following Megatron is the school of hard knocks, then Starscream is the valedictorian—but not without a few scars. Starscream may have once been compassionate, he may once have known what true friendship is, but all that has been replaced, scab for scab, with the lessons of Megatron's abuse.

Unwittingly, Megatron may have created a monster even he cannot ultimately control.

Starscream's nominal Micron (Mini-Con) partner is Grid (Swindle), though he has been seen to work with Zapmaster.

(Source: Transformers Wiki)