Oh, well.
When she has mentioned that dialogue, shortly after, Squall then said that he want to be her knight (I can't find the dialogue). I find that quite overwhelming because earlier in the game, Seifer said he also wanted to be Edea's knight. I know, it's natural for Squall to protect Rinoa because he loves her, but using the "I want to be your knight" dialogue or something similar is just strange. Wrong translation from the japanese version?
Rinoa
"Nobody would want to be around me anymore..."
"The sorceress will be seized upon arrival. Be sure to follow the crews
instructions."
Rinoa
"I'm...scared."
"Squall, do you copy? Is the sorceress listening, too?"
Rinoa
"I'm scared, Squall."
Rinoa
"I don't wanna go back."
End Scene.
I don't know what to do...
This is just another crossroad in my life. But, for the first time, I don't
know which way to go.
I've come this far because I've...fallen for you.
......Rinoa......
Now...am I just supposed to let you go...?
Scene: Esthar. Rinoa and Squall exit the Ragnarok, and are met by some
Esthar men.
"Sorceress Rinoa."
"Hyne's descendant."
<Rinoa goes to them.>
"Come with us. We must seal your power for the sake of the world."
Rinoa
"......All right."
After Squall saves her from the whole sorcess sealing thing, he thinks to himself.
Squall
(Rinoa......)
(Even if you end up as the world's enemy,)
(I'll...)
(I'll be your knight.)
After searching all the scripting after Rinoa became a sorceress, she never asks him to be her knight, it just ends up Squall's personal decision that he stays too and I'm pretty sure she knows it anyways.
As for Seifer loving Edea, like it was said in the Rinoa finger-sign thing, the sorceress can control her knight, so becoming her knight may or may not have been his choice. I think it was more like brainwashing and picking at psychological damage as shown by the scene where he willingly goes with Edea after she talks to him.
<Seifer leaves, dragging Deling with him. Quistis runs after him.>
Timber-TV Station-Back room
Seifer
"!?"
"...Poor, poor boy..."
<A strange woman comes through a wall.>
Seifer
"Stay away from me!"
"Such a confused little boy. Are you going to step forward? Retreat? You have to decide."
Seifer
"Stay back!"
<Quistis enters, but the woman uses magic to knock her down.>
"The boy in you is telling you to come. The adult in you is telling you to
back off."
"You can't make up your mind. You don't know the right answer."
"You want help, don't you? You want to be saved from this predicament."
Seifer
"Shut up!"
"Don't be ashamed to ask for help. Besides, you're only a little boy."
Seifer
"I'm not...Stop calling me a boy."
"You don't want to be a boy anymore?"
Seifer
"I am not a BOY!"
"Come with me to a place of no return. Bid farewell to your childhood."
<Seifer lets go of the president, and Deling runs away. Seifer waves as
Squall, Zell and Selphie enter. The woman uses magic to paralyse them.
Seifer and the woman walk through the wall.>
All full scripts can be found here:
Script and FMV descriptions - Disc One (http://www.rpgamer.com/games/ff/ff8/text/script/ff8d1script.txt)
Script and FMV descriptions - Disc Two (http://www.rpgamer.com/games/ff/ff8/text/script/ff8d2script.txt)
Script and FMV descriptions - Disc Three (http://www.rpgamer.com/games/ff/ff8/text/script/ff8d3script.txt)
Script and FMV descriptions - Disc Four (http://www.rpgamer.com/games/ff/ff8/text/script/ff8d4script.txt)