Why did BJP call Nitish `Opportunist`?

NDA and JDU alliance broke in Bihar. Nitish Kumar has submitted his resignation from the post of CM to the Governor. So far, 1-2 ministers have formally responded on BJP's behalf. But the way Nitish Kumar has broken the alliance with NDA in Bihar, what will be its effect on BJP in the coming time, at the state level and also in national level politics, BJP talked about these issues by holding a press conference.