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Oh jeeze, I had the best response planned and it said I wasn't logged in.
Four paragraphs, gone,
Anyways, in summary (A really bad and less explained one, sorry, it made alot more sense before, but alas..), he's selfish for his own life because he would easily kill someone who threatened his existance because Lelouch is alive. If Lelouch was dead, he probably wouldn't put up much of a fight.
Like how he killed Shirley because;
A.) She regained her memories, and should she have been allowed to talk to Suzaku about it, he would assume Lelouch got his memories back aswell, then he would suspect Rolo was hiding it, or had a hand to play in it. So all three of them would probably end up dead in some way. So she was indirectly, to him, threatening his own life. He took offensive and decided she didn't need to be there because she posed as an accidental threat to him and Lelouch. And again, if Lelouch was killed he would lose anything he had to go back to, emotionally.
B.) She 'threatened' to take Lelouch away, but he took it waaay more radically than it should've been taken. His reason to keep living would've been pretty much taken away. However, this I still don't understand because he seems to think fondly of the idea of having a family and didn't have a negative reaction when Milly said Shirley might become Lelouch's wife.
He's selfish because he would have no problems throwing a knife in Marrianne, should she still be alive, if she threatened to kill Rolo, or take him away from Lelouch. He doesn't like people threatening Lelouch's existance, he takes it as an attack to his own existance.
So he is selfish for his life in the sense he would ruin Lelouch's, probably accidently, not intentionally, if Lelouch was threatened to be taken away from him.
Ouch, I guess your right about the meaning of his life thing.