The breaker-upper generally wants to break up right? I mean, that's why they are the breaker-upper.
[0] Those lasting more than a few weeks, or with a more deeply felt emotional connection. Most likely also a desire to have a future with the partner, and not just a series of dates and screwing and then drifting away to find someone new.
People can have mixed feelings about a relationship/SO, especially as the relationship ends.