Sometimes (always), I like to think that if there really is an "afterlife" in the wizarding world, Gellert and Albus are together.
Not in the sense of them meeting again after death and everything being fine—no. Rather, in the sense of Albus repressing those feelings for the sake of his family, for Ariana (even though he never asked her about it), but feeling terribly guilty knowing that Gellert is out there, as free as possible. Yet he can't go looking for him because it would feel like a betrayal, and the weight of it worsens every day.
Gellert, on the other hand, tries to change. His hatred for Muggles may not turn into love, and maybe it never will, but he tries—for Albus. Because he feels that Albus is the only thing he wants to live for. He wants to be with him, but he also knows it's too late. Albus is no longer looking for him, and although at first, Gellert refuses to accept it, in the end, there's no choice but to come to terms with it.
If things were different, maybe he would have gone to Albus, begging for another chance, for them to be together again. But he knows Albus is with his family now, and he doesn’t want to ruin that—he doesn’t want to ruin Albus’s life again. (Besides, if he were to see Ariana again, he wouldn't be able to look her in the eyes.)
I also like to think that it was Ariana who realized Albus wasn’t okay. Even though he tried to pretend, she knew. I suppose there must have been a breaking point when Albus finally told her everything—how much he regretted being so selfish with his feelings, how he couldn’t stop thinking about them, even after his wish to be with his family and earn their forgiveness had come true.
Ariana, of course, isn’t happy about the idea of Albus being with the person who destroyed what little remained of their family. But she understands her brother. In a way, she gives him a kind of green light to go find Gellert—though not without long conversations with the whole family, many doubts, and, ironically, being pushed by them to go after him. Because they know what makes Albus happy. They know the part of his heart that is still missing.
The process is long. Nothing becomes stable or good overnight. There are conversations, doubts, and fear. But, in time, things get better, and they both find happiness. <3
(At that point, everything starts improving. Ariana may have seriously threatened Gellert in case he ever hurts her brother again, but all is well. I actually feel like they’d get along, and Gellert would help Ariana with any questions she has about magic—another headcanon I have, but this is already too long.)
I've had this idea in my head for months, I needed to say it 🙂↕️