You need to know how to break up with a woman in a nice way. Whether the woman is a complete mess or the nicest person in the world, leave the relationship showing your respect for her and the time you both shared together.
Okay, in many cases, you don’t have to be nice. For example, if she cheated on you, then you don’t have to break up with her in a gentlemanly way. But generally speaking, when breaking up with someone, it’s because you don’t see them as someone you want to spend the rest of your life with. And these reasons don’t validate you acting in rude or disrespectful way.