Because nox still have the curse and amy knows that selena and only selena can cure him and if she gets in the way (if she will not run away) nox's curse will never be cured because we all know that when amy is there, nox's attention is all her's :))
And Amy also have another reason why she's running away, it's because she and and her sister (Diana or dian idk) have bounties in their heads. (Amy’s family are powerful/genius nobles from what I remember).
I get that but she’s so stubborn when she knows he’s absolutely loyal these are all issues that can be solved with just a little communication that she refuses to do. She could even give partial stories and not the full truths to expose things but she just constantly runs away and then complains about being sad it’s super frustrating T~T
I don't get it. Why do she need to run away?