Also, Rowling has never said that Grindelwald was Dumbledore's lover. Fandom made the leap from a simple "Dumbledore loved Grindlewald" to "they were shagging like bunnies". Grindelwald was aware of his friend's feelings, and exploited them. Of course, that's still open-ended enough to allow fans to continue their field day.
Rowling: I think he was a user and a narcissist and I think someone like that would use it, would use the infatuation. I don't think that he would reciprocate in that way, although he would be as dazzled by Dumbledore as Dumbledore was by him, because he would see in Dumbledore, 'My God, I never knew there was someone as brilliant as me, as talented as me, as powerful as me. Together, we are unstoppable!' So I think he would take anything from Dumbledore to have him on his side.