I am quite into the story of the Awoken race and what was happening to our favourite Awoken characters during both Destiny games and one thing that bothers me is how close were both Cayde-6 and Uldren to Petra from what we can gather.
Petra and Cayde felt almost like a fireteam, working together in a pair anywhere they could on the Reef, even communicating secretly between Reef and Tower when they could and Cayde expresses feeligs of strong friendship he had with her in one of his Ace of Spades mission chests. His death was something that made her not question killing Uldren in revenge, even tho Uldren was her close friend as well.
But is it possible that she was prepared to kill Uldren not only for revenge, but out of sorrow of turning him against her? There are clues leading to Uldren and Petra being closer than one could see, even tho there is not much of them. But in one of Lore entries we could learn about how painful it was for Uldren to give up on Petra during his secret plan with Scorn, while Petra is described as being joyful and then depressed after the return of Uldren and revelation of him going crazy, talking about Mara being alive.
Important nod to all of this is in Black Talon's tab, describing Petra as a broken person, that wants to believe that both Mara and Uldren are alive, so much that she is unable to join *Uldren's* memorial. Another thing is her own quote: "Even if I can't excuse his crimes... I sometimes miss him. I can't help it." He was close to her. Definetly. She always felt proud to be under command of Mara and Uldren, both talking casually together about things and news when these two could, she sometimes quoted his feelings about Guardians back in D1 and seemed really into what he says.
So my conclusion is that when she decided to kill Uldren, it wasn't just because he killed Cayde, she mentioned that the Ghost, who knew what Uldren did to Cayde, didn't know what he did in reality. What I think what he did in reality was breaking her completely, most importantly her affection and trust in him which actually hurted her more than Cayde.. then of course there is this thing with annihilation of The Awoken which Uldren also did, which could set her off, but.. if it was about that, I think she would definetly antagonize him more like Adolf Hit--r and spit on his grave whenever she could.
But since she felt strong connection to him, I think that she actually wanted badly to excuse his crimes and have reasons not to kill him, but it was like breaking the closest and only friendship two people could have, maybe even a romance, but definetly only on Petra's part. Uldren probably was closer with his friend with which he entered Black Garden than with Petra, tho I don't believe those two were romanticaly involved like some people point out.
Lore masters, I call upon you to help me out with this soap-opera thing that I am probably digging too much into, and help to resolve if it was Cayde who was closer to her, or Uldren. :D
Also, do you think that it will move in some way with Petra when she finds out..
WEEELL - SPOILERS - SPOILERS - SPOILERS
..that Uldren is alive as a Guardian, so a good guy again, but without any memory of her and of Mara? [/spoiler]
Uldren wasn’t revived. That was a scrapped cutscene made to come out at the end of Forsaken but they realized how stupid reviving him would be so they scrapped it. Petra cried for Cayde when he died, Petra put a bullet in Uldren. Kinda shows who she was closer to.