I don't really think that Itsuki has been manipulating Mao. She is just smarter than Mao thinks, and also choses to stay in this situation and not move on from Mao. She likes her and probably finds it less painful to try to move on, unless she really needs to.
Mao is attracted to men but hasn't fall in love with one, yet the exact opposite happens with Itsuki. Besides the fact that this is also an orientation (if she is trully heterosexual but homoromantic) I believe that maybe this could also be a mechanism for her to stay away from getting too close with someone. Like being with someone but keeping an emotional distance at the same time.
The way this ends, I do believe that at some point they will eventually drift apart. Itsuki will probably realise this goes nowhere and will end it. Maybe Mao will get even more desperate then and even try to sleep with her, but Itsuki will see how this can't work.