[Like many others, the first place Yukine plans to check out is his new house. He's sad the house Snow and David had, where he lived in, is now gone. It feels like he lost them for good, in a way.
With everything that happened, the world changing and trying to make some sense out of these changes, Yukine hadn't noticed that Sakura went home. So when he sees her he thinks it's something this world is doing to mess around with her.
His first reaction is to draw a line, trying to hit the butterfly or at least get it to let go of her.]