Why do people marry shortly after breaking up with someone in a long term relationship?

It’s happened time and time again, the couple are together for so many years without marriage, then they break up. One of them (usually the guy) ends up marrying some random women he’s only known for certain amount of months. I mean look at Selena Gomez and Justin Bieber they went through the same thing. I wonder if people who do this are miserable
Why do people marry shortly after breaking up with someone in a long term relationship?
Why do people marry shortly after breaking up with someone in a long term relationship?
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