[Setsuna knew the other liked the pink haired pacifist. That much was obvious information, and he knew they had... done things the night GIR took over if Tieria's reaction from the phone conversation was anything to go by. Certainly they spent nights together. He had pieced as much together on his own, though of course he never let it on he actually knew anything or acknowledged it.
In some ways, he didn't like that he spent so much time with Lacus. Neil had died and been taken from them and he was suddenly back, and yet he chose to concentrate on this pink haired woman. It was like a little brother, jealous of his older brother's new girlfriend and loosing their special Saturdays at the ball game or something.
But he also knew, deep inside, that if he ever got sent back, Neil... was not going to be there. It was that thought that had fueled his initial clinging to Neil and his outright dislike of Lacus. And then it had turned into could he go through connecting with Neil again only to be sent back and look at the face of his twin and know it was all a dream?
He looked at Neil for a long while, though, and finally opened his mouth.]
I know you like her. I've known for awhile.
Be with her, if you want. But, she is not a Meister. She was not CB and she never will be.
[In other words, she wasn't us.]
Do as you please with her. But do not expect me to treat her like one of us.