He took the energon out to make sure he died, right? Also he was constantly plotting against him and shit.
Anything to lead, until it was too hard to do and he realised he should just accept Megatron as his husband. Didn't ol Megs kill Dreadwing for Starscream anyhow?
I do wonder if he'll turn up in RiD again, after Screamer was acting like a jilted ex over him.