I'm not exactly sure who this song is about, but the obvious answer would be Gigi Hadid of course. Zayn and Gigi recently had a baby daughter, which is adorable. But the couple has a long history of breaking up and then getting back together. They did this in 2018, and then again in 2019. I believe that Zayn is addressing why they broke up. He is saying "Gotta let it go so your heart don't break" which means that although he broke up with her, it was primarily because he loved her and did not want her to get hurt.