[ At the moment of "he's straight", Souji's smile fades and turns into a small frown. He leans back and then crosses his arms, thoughtful. ]

... Mm, I remember his response when I told him who his date was. [ According to Yu's tone, it seems like Souji doesn't have to explain what Yosuke's response was (spoilers: it was a lot of capslocking) ]

How did things get weird at prom? When he thought you and Karkat were dating?

[ He doesn't answer Yu's question just yet. He wants to ask this one first before he gives his thoughts. ]