Well, as some already intuit, this is simply an AU (?)
I like the Ship of RoyEd (In any form, be OTP -which is- brotp or parental) and I have my own headcanons and AU to be together (?)
Here Edward is already Colonel (rank that he has in the game of Bluebird Illusion) and Roy is Führer, of course, who is the Roy of 2003 who has the eye patch (As we already know, we never looks like Roy looks without the patch , so on my own initiative try to imagine how he would look without the patch, he would keep some scars on that side of his face that he won during his confrontation with King Bradley -O Pride in 2003- and added to the loss of the eye, a scar that covers the eyelid and the white pupil in a sample that does not have sight in that eye)
The image is basically that Edward is going to wake up Roy to his bedroom in the military dormitories (Roy several times would end up sleeping there for the convenience of not being late to work xD) since Edward ends up being the secretary of the Führer (Fact that also happens in Bluebird Illusion xD)
Btw, sorry if something is not understood, it’s late and I’m kind of tired (?)
Every time I see someone describe Roy as a “womanizer” (especially to suggest he wouldn’t be loyal to Riza) I want to find the nearest grassy knoll and roll down it forever just to put as much distance between myself and that concept as possible
The boy goddamn grew up with an adoptive mom who used her “girls” to run a covert information-gathering network because they were rarely suspected as more than curious, flirtatious, naive young ladies–it was a front, a ruse, a clever tactic using young sexuality to disguise illegal information reconnaissance. Roy encodes his alchemy notes as “date journals” which no one besides Ed and a close few seem to know because that’s the point of encoding things. To keep them hidden. Roy doesn’t actually date any of these girls; he puts on a front, makes himself seem like all he cares about is chasing tail to disguise his truer, subversive goals in the military. He intentionally pisses off his less important underlings with loud flirty phone calls (spoiler alert: to Riza in disguise) in order to further this mask so he is viewed as less of an ambitious, focused threat. Roy never actually dates anyone ever in the entire series. Not in flashbacks, not currently, even when Havoc makes it clear it’s an option. He only ever flirts with “Elizabeth” which, spoiler alert, was another front he used to keep up conversation with Riza while they hunted out Gluttony. He flirts with and gives flowers to Olivier as a means of revealing the secret identity of an all-powerful homunculus who can observe everything from the shadows. It’s all calculated. It’s all intentional. It’s all a huge freaking subterfuge.
TL:DR The only times Roy Mustang has EVER exhibited womanizing behavior was to trick other people into ignoring his highly illegal, societally subversive, ambitiously driven attempts to overturn the entire structure of Amestris and if you think it’s a genuine part of his character than boy oh boy he’s tricked you too.