I'm not taking the governor-general's words on this one. He's quite biased and it's also probable that Arika is only assumed to be Negi's mother. Unless Nagi himself says so or there's conclusive evidence that leads to that kind of conclusion, I'm going to take Godel's words with a pinch of salt...
Well Kono~chan and Secchan have tried making a pactio before but you should recall that Asuna kinda walked in on them before they were able to do it