MC doesn't automatically fall for the FL, she just wants to live in peace. Her last life s**ked, so in this one she just doesn't want to be targeted. But she's also not vile, she couldn't just let the FL be taken advantage of by the ML. There are so many moments she regrets saving the FL thinking she's not a hero, she doesn't want to get justice for anyone she just wants to live in peace without anyone trying to kill her. But she can't stop herself from thinking of the FL. She doesn't have the power to help the ML. That one time at the start was risky as hell hiding the FL from the ML. After that the FL has been helping MC because she's grateful. But FL has also struggled with the loss of family. MC shouldn't have felt anything after all she's not a hero, but she can't help but send her ginseng spirit demon thing to keep FL company. At first she thinks ok I just want her body, but then she realises she just wants FL not to be used by anyone. So she ends up letting herself be used by the female demon lord.

about the female demon lord, MC thinks the female demon lord Li Hai just wants to keep the demon seed by her side, she's just possessive, but what MC doesn't know is that Li Hai has actually fallen for MC.

So the ML is from the same world as MC. ML also not not a good guy. He knows he transmigrated as the ML, and he thinks of the FL as his possession. He commits a lot of evil acts. That's why MC doesn't want the FL to end up with the ML, but also MC worries about her own survival because ML is cruel and selfish who would definitely kill MC if he finds out she's the one who saved the FL from being taken advantage of that one time. Eventually though he figures out she's the reason he couldn't get his hands on the FL. He still uses underhanded methods to get his hands on MC and torture her.

Just as ML thinks MC will die and he'll win, things go wrong. FL is destined for greatness, of course she thwarts the great evil about to go down. Not only that she's able to rescue MC. There's definitely some bed scenes between MC and FL. But the ending is mostly MC working to revive FL's older brother. MC just wants FL to be happy at this point. She succeeds. It's pretty peaceful. Li Hai the female demon lord is defeated and vows revenge but it kinda ends there. MC has a female disciple who's in love with MC but disciple also just wants her master to be happy, so... She sleeps with Li Hai since that's the closest she'll ever be physically to the master she's in love with. It's not clear what Li Hai will do in the future, but I ship the disciple with Li Hai.