One of, if not the most important, skills to playing Yuumi is attaching/deatching at the right moments to maximize passive use and weaving in autos while maintaining safety. However, I have found that mechanically it can be a little "wonky" at times especially in teamfights to control. It happens far to often that I change attach points rather than detaching and detaching when I want to change attachment points.
My suggestion is to make it so casting "You and Me" only attaches/changes attachment points. Detachment would now be controlled by issuing a movement or auto attack command. Ideally, the movement/attack would immediately happen after the detach animation for added smoothness.
TL;DR: Yuumi W is only for attaching. Detaching is now controlled by right-clicking.