If you have to stop your coroutine, you probably should not be using a coroutine.
Coroutines in a nutshell:
Splitting up larger tasks in coroutines:
Coroutines are NOT always an appropriate solution: know when to use them!
“Why not simply stop having so many coroutines ffs.” - orionsyndrome on Unity3D forums
Our very own Bunny83 has also provided a Coroutine Crash Course: