How long has she waited to make this decision? I would absolutely laugh hard if she came around and Yuu was like, "sorry, I got over you."
The main character's romance in Kindred Spirits was the same way. "Ah yeah, Imma keep her waiting for like a month, don't worry, she loves me, she totally won't get disgusted with how indecisive I am!" That, at least, had the main character say she wanted time to think about it. Here it looked to Yuu like touko turned her down.