It isn’t really confirmed, but I wrote an analysis about a year ago (shortly after Uprising) on the relationship between Morrison, Reyes, Amari, and what could have possibly drove the two men to fight each other, when in Uprising, they’re still shown as companions. It was long after I wrote it that Jeff came out and said it wasn’t the promotion [of Morrison to Strike Commander] that separated them, which only further proved my original point. Because honestly, if Reyes was upset about a promotion, why did he stick around for another twenty years pretending to be all buddy-buddy? But I digress.
To summarize, I’d like to think it was the death of Ana Amari, and the fact that Morrison left her there, that drove a stake between them.
Reyes, in his Blackwatch experience and choices, was always willing to give people second chances, and was probably always breaking the law by doing it. Genji, the son of a crime lord, was thrown into Blackwatch when he should have been arrested or killed. McCree, who should have been arrested, was given the chance to enter Blackwatch because Reyes saw potential in him. Moira, after being fired from Overwatch, was met with open arms by Reyes, who allowed her to experiment in whatever amoral ways she saw fit. None of those things are necessarily legal, or even a good decision.
But, the point is, Reyes never left anybody behind.
Jack Morrison left Ana Amari for dead in Egypt. Regardless of the context, you know Reyes would have delayed departure until everybody was on board, especially if there was a chance to save them. Reyes was all about chances. Morrison? Not so much. He was a Decisions type of guy; he preferred to sit back and make a choice, then follow that choice. [See Uprising, when he debates whether or not to engage in King’s Row in the first place. Meanwhile, McCree was already there under Reyes’s command.] Morrison thinks something through and is sure of his intentions before engaging, instead of “Let’s give it a shot even though we’re unsure, see how it turns out.” Reyes, of course, is this latter statement. Yet again, I’m getting away from the point.
Morrison leaves Amari, completely unaware of her well being, and doesn’t think twice about leaving her there. They’ve been partners for thirty years! She could have been completely uninjured and he still would have gone. Duty aside, that’s a pretty crappy thing to do to a lifelong friend, especially when there was a chance to retrieve her. So, when Morrison returns to the base and Reyes hears the news that, not only was Amari left behind, but that they don’t even know if she’s alive? That his best friend just decided to leave her there? Again, duty aside, to someone like Gabriel Reyes, who would have taken that chance to get her to safety, Morrison’s action is unforgivable.
This, the blatant disregard for their best friends’ life, the chance to save her ignored, is what I believe drove the two men so far apart.
This got a lot longer than I intended, sorry about that. But I hope you enjoy the theory.