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Big spoilers here
Nina loves Sett, she even told him in the latest chapter. She refers to Az as her first love, and he is important to her, but not as a lover. Again, pretty big spoilers here, but the important reason why we had to know who Nina loves is because that person has to kill her when her powers go out of control. So even if Nina loves Sett, their time together is limited.
Also, you can read this manga for free on the official Km@nga app (Kod@nsha's manga app). You can get points by scrolling through a given chapter each day, and you can also watch 3 ads. It doesn't take up much time and you can read anything on the app for free if you have the points or daily tickets. Finished series/some shounen titles can be mostly read with daily tickets. So you can support the author legally for free.
If you have the Webt@@n app, change the content language to French, you'll find the series on French Webt@@n. Subscribe to it, and like all the episodes, you can even leave comments, this way you're supporting the creator and they might be able to finish the story.