Young!Royai is adorable and pure and everything and I love the idea of them falling in love as awkward teenagers but then the manga quietly reminds me that Riza addresses Roy as “Mr. Mustang” when they’re standing alone in front of her father’s grave, which makes it pretty clear to me that there were no romantic attachments at the time. Of course, I’m not sure what the original Japanese was, if it actually translates to “Mr.” or if it was something less formal. But regardless, the manga makes it explicit that they were close enough to share personal feelings but not so close that Riza felt like she was allowed to use his first name. So, friends, probably, but lovers, no.
(Unless cultural norms are just that wildly different in Japan and if that’s the case someone please tell me so.)
And while that makes me pretty sad because I think their relationship would be even more bittersweet if they’d been in love before the war, it also makes me excited and emotional because that means that sometime between her father’s funeral and her graduation from the academy a couple months after the war, their feelings for each other went from “we lived in the same house for a few years and got along well enough” to “I feel like I can trust you” and “I’ll follow you into hell if you ask me to.” I have a mighty need to know what happened between them that caused this shift and how long it took for them to recognize that it was mutual and if they ever even had to say it aloud at all.
I would give an arm and a leg for a sequel series that solely explores their relationship pre-canon and post-canon.