breakup
The end of a romantic relationship between two people.
A breakup is when two people who have been in a romantic relationship decide to stop being together. When a couple breaks up, they're no longer boyfriend and girlfriend, or husband and wife. The word captures that feeling of something whole being split apart.
Breakups happen for many reasons. Sometimes people realize they want different things, or they've grown apart, or they simply aren't happy together anymore. While breakups usually involve sadness and hurt feelings, they're a normal part of life. Not every friendship or relationship is meant to last forever, and sometimes ending one can be the healthiest choice for the people involved.
You might also hear about breakups in other contexts. When a rock band breaks up, the members go their separate ways and stop making music together. A business partnership can break up when the partners decide to pursue different paths. The Soviet Union experienced a political breakup in 1991 when it split into separate countries.