User blog comment:SpookyBoogie27/Light Novel Spoilers/@comment-3965848-20140517112125/@comment-50.172.213.125-20141207201202

On top of that Irina and her family moved away when they were still just little kids and Ise hadn't seen her in years. And she hadn't had any sort of contact with him either.

Therefore, if he is against it Irina's father can't really complain about Ise choosing Rias over Irina if they haven't been in contact with him for so long. They can't expect him to spend his entire life waiting for someone who might never have come back.