Amano really does pick troublesome and problematic women (Older woman that is into NTR people...). IT would be fine if Amano was built that way for open relationship but she is forcing herself like MC said (Not looking happy and just trying to find comfort and affection from other people in fragile relationships)
MC only had two rational choices right now....
1.) Become a true dom and tame Amano to make it where she falls in love so deeply and obsessed with MC that she can't live without MC [Both satifying her revenge act and making Amano life better being with someone that actually cares about her besides her stalker roommate that got too attached]. This route is much more amusing, entertaining and fun.
2.) Just leave and try to forget about her, easier said than done but picking number 1 means getting into more drama and conflict while trying to tame and make Amano her pet doggy.
3.) Just tell Amano to go to therapy, her choice to take it or not. Same as option 2 but just some friendly advice...MC doesn't have the money to hire private instigator to become a shadow lord mastermind to find out everything and plan everything out to the ending she desires afterall for option 4th lol.