Not gunna lie, I really ship Luna and Sombra, especially for the potential they could of had as double-reformed villains bonding over their mistakes, regrets, and how shitty other ponies are to them because of them.
In the episode “The Crystal Empire, Part II”, you see Sombra destroyed at the end, but his horn is still in one piece. I headcanon that he’s eventually reborn from his horn, albeit much weaker and without any of his memories. He’s banned from ever entering the Crystal Empire (except whenever Cadence needs access to his secret parts of the castle, and even then he is under heavy supervision and has to wear a disguise so the crystal ponies don’t panic at the sight of him.
Luna is very protective of Sombra after he’s declared fully reformed, especially as their relationship blooms. She knows how harsh ponies can be towards one with a dark past, having had a hard time adjusting after being turned back from Nightmare Moon. Sometimes she can get a little… aggressive in her protective displays, but she just wants Sombra to know he’s not alone.
Sombra truly is reformed here though he can still use some of his dark powers (such as turning to shadows and using dark magic to create black crystals and access his secret parts of the crystal empire). He’s more than content to live out the rest of his life on the sidelines. While their declaration of engagement was met with mixed reactions, the wedding went off without a hitch and Sombra was declared Luna’s Prince Escort, and given the prefix title “Prince”. A step-down from “King” that he graciously accepted.
