Not Christian myself but I did pick this up from the old forum that made me look into it a bit more.
As Genesis 5:1-2 shows, God made us in His likeness as male and female, so my twin and I aren’t just two random souls who met - we’re one soul experiencing a divine split. In Matthew 19:6 Jesus said: “they are no longer two, but one flesh”
The term “twin flame” is modern but the idea has been around since before the Bible so I’m not surprised to see references like this.