Is this girl not destined for me, or is she destined for someone else, and is there any hope of getting her back after it's too late?

Everything that happens in the universe is by Allah's decree, and the destinies of creation were written fifty thousand years before the creation of the heavens and the earth. Belief in divine decree prevents sorrow and despair, and motivates a Muslim to correct their mistakes and strive in their efforts, then to surrender to the belief that what Allah has decreed is the best. Do not preoccupy yourself with knowing what Allah has written, and instead seek a woman of faith and good character. For Allah alone knows what is good; you may dislike something which is good for you, and love something which is evil for you.