Does this perhaps mean that Kasumi...

Wasn't hurt because I referred to her as just a friend...

But she's hurt because I said that love between two girls is impossible?

What Kasumi wanted to hear...

... is how I really feel about love between girls?

That would mean...

Kasumi made it for you, Acchan.

when Kasumi sees Acchan getting friendly with other people... Kasumi would feel strangely irritated...