Gilbert is honest to God terrified to tell the others that Germany, is in fact, Holy Roman empire.
He wants to tell them that he still lives, but is scared to do so because of the HUGE time period that he didn't tell them the truth.
Elizabeta was a motherly figure to HRE.
Roderick was a Older brother/Uncle to HRE.
Feliciano was their lover.
He is terrified that if he told the others over centuries of not telling and the suffering they have endured of that, that they will never forgive him for what he has done.