Where does the love go after a break up?

What happens to the love when you break up with someone? Why do break ups always have to end bad? I mean of course you and the person broke up for a reason but why does it have to get ugly? Like why can’t two people just be done with each other and go separate ways. It makes me feel like did I ever know this person at all? And it really makes me hate the type of person I become when I interact with this person. If you can be cruel to someone just because you broke up does that mean that you never really loved each other? Or is it that to much bad has happened that the love went away. I’m really not sure. It just seems like certain things shouldn’t be said to one another to someone you have claimed to love.