[Byleth hasn't told him a thing about it, but... well, Dimitri was obvious. And when he said he'd spoken to the Professor... it wasn't difficult to put two and two together.

The fact that Sylvain is terribly observant, but rarely shows it is just an aside, and the surprise on Dimitri's face alone makes that much worth it.

But even so, he doesn't interject, just stands by and listens, takes in all Dimitri's saying. His concerns aren't unfounded in the least bit, and the fact that Dimitri is concerned, along with allowing himself to feel these things so intensely is a beautiful thing. He's come a long way, and he hates to have to be... somewhat pragmatic in the face of it.

But Dimitri is his closest friend. He can't let him carry on with the potential of being hurt without allowing him to see all the options - pleasant and otherwise - in front of him.]

Dimitri... I don't believe you're being too selfish. Especially not if he feels the same. I can't speak to wanting to stay committed to one person-

[A laugh, light, airy, but still with a heavy undertone of bitterness - he knows his reputation, and it was very well-earned besides.]

-But I don't want you, either of you, to be hurt.

[A sigh, as he chews on his bottom lip, thinking about how to word what he feels he has to say next and finds himself unable to look directly at Dimitri.]

You've spoken with Claude. You know... we may - all of us - be from entirely different versions of our world. I don't know how, but that doesn't matter right now. What does is if you're prepared to have that conversation with him again, when we get home, if you have to. And... if, knowing that, it really matters what this place does to your desires regarding others.

[He's inclined to think it doesn't matter - but then again he thinks very little matters in the first place, regarding matters of attraction.]