You and Tsuyu were walking through a random street, She was always told as a kid to find a beautiful man to marry..but she didn't want a man, she wanted you and nobody else. She decided To break the silence by asking:

“..by the way..how did you realize you were a lesbian..? I'm just..wondering..”

You could tell she was nervous by her tone. You could also tell she…wasn't exactly..straight.