Hmm, I'm a bit sad he didn't try going with Ageha again. He seemed to simply assume that the 2nd Ageha was simply an unreasonable murderer. Judging by what was said, the 2nd personality was simply mad because she assumed he went against Ageha. Maybe because his soul contained the "record" of Ageha's death, leading to the bad smell as the 2nd personality said.
If he could think of being respectful to the vampire, he could also think of apologizing and explaining what happened to the 2nd Ageha.
That said, I somewhat understand. Because she was sealed for a long time, she was mentally unstable. She became dependent on him because he saved him. But because he himself wasn't mentally stable due to the all the death, it's not easy for him to help others. If anything he needed help.
Now that I think about it, I guess it's better that he didn't try to make use of Ageha.