Grandpa is such a spiteful ass, didn't approve of his daughter Kyouko decision, even knowing his business will go to the shareholders, just because she chosen a "commoner".
Reasoning behind Eiji "breaking up" is to not loose the house his mother and father lived, he is technically the owner but under condition he won't marry Aoi. But even if he will eventually be able to support his house, Aoi waiting for him is pointless because he will loose the house nevertheless. Seems like a moot point...
Maybe through Eiji another selfless sacrifice will break the cold bastard grandfather heart, I get to achieve a rule of a company is to be stubborn but there's limits...