You want it to appear at the start of every faction's turn? Including the AI ones? For every turn that the Greeks hold Lilybaeum?

Well, okay, try this trigger instead:
Code:
;------------------------------------------
Trigger 2902_Sicilia_Casus_Belli2_Trigger
    WhenToTest FactionTurnStart

    Condition I_SettlementOwner Lilybaeum = greek_cities

    AdviceThread Sicilia_Casus_Belli2_Thread  0