People like to talk about reading too far into things, but I think it can be interesting (and even telling) to see what you can find if you only pay attention. When I first joined fandom for FMA, I noticed that people (for every ship) liked to go back to the Japanese raws and dissect the original language. After all, lots of things are lost in translation - one of which being the Japanese honorifics/social hierarchy/pronouns. In these cases, there are literally 10 or so words for the word we just call “You” and it matter who says them, what word it is, and to whom they say it.
In this case, blink and you’ll miss it. Hell, unless you knew Japanese, there was no way to read this English scene as anything other than exactly what it says. “Not again! You need to worry about yourself! Your eyes—”. But in Japanese, Riza says something with an entirely different flavor. This is in fact, the third time she’s addressed Roy without formality and directly. Riza uses “貴方” (あなた/anata) to address Roy. Which, if Roy said that to Riza, it would sound completely fine - he’s her superior officer, it would sound formal/normal. But “貴方” used by a woman to a man is anything but formal: Anata is commonly used by women to address their husband or lover, in a way roughly equivalent to the English “Dear” or perhaps “Honey”. In fact, we see another couple use the shortened (even less formal) version of Anata, Anta: Izumi addresses Sig by “あんた.” which is more like “Hon”. These are always intentional with Japanese authors and they always mean something. Izumi using Anta lets us know she’s a casual sort of person, openly affectionate with her husband. Riza uses Anata three times - twice in Chapter 95 and once in the above moment where she’s reunited with blind Roy.
“You only want to kill him to satisfy your own hatred!”
“Please Colonel…Don’t you go where I can’t follow.”/”…Don’t you fall that way.”
Incidentally, after she addresses him informally twice, he also drops his formalities, and uses “君”/”きみ”/kimi instead of “Lieutenant”. Kimi is less telling than anata, but still: “It is informal to subordinates; can also be affectionate”. Given the context Roy uses Kimi in, informality and affection makes sense:
“What will you do after I’m dead?”
“Unacceptable. I won’t lose you, too.”
You’re right. In the English version these two call each other Colonel and Lieutenant, breaking it once for Elizabeth and Roy. They address each other as “You” which only has one connotation ever. But in Japanese where you need no subject in a sentence for it to make sense, and thus no pronoun for a sentence to make sense, the use of informal pronouns (commonly used by lovers/wives) is a really big deal with she puts a gun to the back of his head, and starts to beg him to not continue. It communicates, A.) The relationship is equal (otherwise it would be extremely rude and presumptuous of her to use it to someone above her in rank and status), B.) She feels the need to address him on a personal level, and C.) Would imply to someone watching that they have a relationship where she has the privilege of calling him so informally/affectionately. When Roy asks her (also informally) what she’ll do after she shoots him, and then continues on to say that he won’t “lose you, too [in addition to Hughes].” using kimi it means A.) He’s returning the relax of formality B.) Is further implying affection towards her, who just stated that she will kill herself after losing him.
If you wanted to know what reading deeply into something looked like folks, that’s it - and not that many people do that. Everything else is just for funsies and character development. And really, what does it hurt? Bet you even learned something about the Japanese language!