Disclaimer: This world belongs to J.K Rowling and Warner Bros.
This fanfic contains spoilers for Fantastic Beasts: Secrets of Dumbledore!
Gellert saw the pendant starting to crack, he felt like everything was over for him. This blood pact was a promise that he and Albus made, when they were together. Does this mean that their relationship is really over now? What held them connected all this time, is now broken.
He found himself in another dimension, a different place than he was a few seconds ago. it was a white dimension, and almost everyone who surrounded him wasn't there, except Albus. They shared a look, both of them knew what was going to happen next, now that the pendant is broken.
They started to fight, shooting spells at each other. Gellert didn't want to fight Albus, but he couldn't forget what happened between them. If Albus hadn't left him, maybe they didn't need to fight now, and they would be together, reshaping the world as they wanted so long ago, but they weren't.
They pointed their wands at each other, and Gellert noticed that Albus' left hand was on his heart, and his hand on Albus' heart. He felt Albus' heart beating, it was fast from their fight, but it began to slow down. He missed him. After everything that's happened, he still loved him, and he could've felt that Albus felt the same way.
They lowed down their wands, still looking at each other, but didn't say anything. Gellert wanted to be with him, but Albus abandoned him. He still remembered what he felt when Albus left, back when they were young, it was painful.
He hoped that Albus changed his mind, no matter how long it's been, he was ready to forgive him, but he saw Albus leaving him again. Did he still not want to join him? Even after they felt each other's heart beating? Did Albus move on? Gellert remembered Albus saying "I was in love with you", and figured that he probably had.
"Who will love you now, Dumbledore?" He told him, heartbroken. He felt betrayed. He tried to feel an emotional separation from his former lover, and decided that from now on, he won't call him Albus anymore. He couldn't, after that. He didn't want that relationship to end this way, but Dumbledore leaving him again was too painful.
Dumbledore ignored him, perhaps decided to do nothing about what just happened, probably denying that moment in the other dimension. He figured that maybe that's how Dumbledore thinks about him now- as his enemy. Does this mean they are now can fight each other, now that the blood pact is gone, and the pendant is broken completely? Gellert hoped it wouldn't happen, but he knew that Dumbledore would come to fight him eventually, he hoped that at least it would be in a long time from now.
Author Note: After I saw the movie, I just had to write this. This scene made me emotional and contains one of the powerful sentences in the movie.
At first, Gellert still prefered to Albus by his first name, because he still loves him. But after Albus turned away from him, it was clear that Gellert was hurt and tried to make an emotional separation, so from then he prefered to him by his last name, Dumbledore.