So, one of the things that hasn't been made clear yet is what exactly Maya did (that made her into a bad person). I was rewatching Noriko's conversation with Maya on the second beach trip, and the possibility for blackmail from Maya increased.
I think it's interesting because this conversation points out that Maya did some fucked up shit to get Akira away from Noriko (actually from Niki and Sekai), and that she was more or less in the same position as Ami in being a child trying to care for a broken adult. She tried to get him to move past them, but he was unable to, so they became these sources of fear for Maya (that she could do nothing about, but avoid).
Overall both of them want him to be healthy, but also not so healthy that he doesn't need them anymore - probably because if that day ever came to pass, then both Ami and Maya would also have to grow, and deal with the fact that Akira may simply not want to engage with them in a romantic manner (he could, but the possibility has got to be really scary for two people that have no one else in the world).