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Amaterasu93 Well Tomoe's objectives is a little bit on the side of her possessiveness of Makoto. All of the things she has done so far is for the good of Makoto. Keeping Rembrandt's secret but keeping an eye of him are all signs of in keeping in mind of Makoto's well - being. Remember, she is in a master - servant contract with Makoto and with that kind of contract, betrayal is nonexistent even if she is a Superior Dragon.
If anything, she wanted Toa to be independent as to keep her away from Makoto and his lingering feelings to his old world as Toa have a semblance to his Kouhai. Think of this way, Tomoe and Mio's affection for him goes beyond a Master - Servant relationship and both wanted to be his lover. Even though it wasn't stated thus far or Tomoe herself have stated it, Tomoe does have the same affection as Mio has. So we can assume that Tomoe have some romantic affection to Makoto at this point.
You can say that Tomoe is on the Clingy Jealous Girl trope except that she isn't the type to show it from time to time except for the one time that she had a rivalry/power showdown with Mio on who's helpful for Makoto. With this chapter, she also has some Yandere tendencies shown with her eyes but remove the "killing" part. Nevertheless, Tomoe just do what she thinks is what's good for Makoto.