>>23409779 (OP)Tomino's writing and storytelling is often very multi-layered, mature, and is very relatable on a human level. So I'll try to break down this scene and it's different human elements. It will also help those who have autism and don't understand human interaction (I've discovered many mecha fans are genuinely autistic, and have trouble with romance).
Breakdown:
Very Deep down Fraw Bo still loves Amuro. It's an open secret that people never forget their first love.
But Fraw Bo is basically resigned to the fact that Amuro will never love her back in any romantic way in this life. Even if it did happen, it's too late because she's "married" to Hayato, and pregnant with his baby. You don't mess with married women.
( I say married with quotes because it seems like their marriage is cold. We never see Fraw and Hayato happy together. Hayato only seemed to lust after Fraw's body. But had no emotional connection with her. He only took care of the kids. )
Back to the main topic. So since Fraw Bo can't Amuro's love, then the second best option for Fraw Bo is to be a good friend to Amuro, and hope for his happiness (and Hope that Amuro can be a good Uncle to the kids). That's why she's mentioning Sayla. Fraw doesn't want Amuro to be alone and unhappy as time moves on.
Haven't any of you been rejected by a girl in real life? Someone you truly loved? Even if she rejects you, most men still think, "Okay. She doesn't love me, but I still hope she lives a happy life. That enough for me to move on in life. As long as she's happy."
( It would probably depress you a lot if you found out the girl you loved and confessed to ended up living a miserable life. Men love to fantasize about saving women and giving them happy lives. )
The irony here is that Amuro actually does have romantic feelings for Fraw Bo. He only realized it after the war was over. But Amuro was too late. Fraw does sense it but doesn't act on it. So the best they can do is a polite goodbye kiss