Never waste your time praying that God change someone's heart or mind or love you again. I know folks like to think that God can do anything, but if he could, wouldn't a power like that be better served ending murderous conflicts around the world instead of your love life? Just imagine, he's about to stop the standoff between North Korea and everyone, but he has to drop everything because you can't accept the fact that your significant other left you. I know lots of people say, "God is Good," but you don't know if God is good at multitasking.
And if he had the power to change hearts just like that, wouldn't you want him NOT to use it? A power like that surely counts as voodoo or witchcraft; tools of the Devil, and using them will condemn him to Hell. All because you can't get over the idea that you're going to be alone again.