How do people move on so fast?/rush into their next relationship?

How do people move on so fast? Did the connection we shared mean little to nothing? When I broke up with my boyfriend (due to age and different life stages) a month later he already had a new girlfriend. We worked together and his new girlfriend was hired a week after we broke up. They moved really fast by dating quickly, traveling and meeting family a week into their relationship. And now I recently found out that after 2 months of them knowing eachother, she’s pregnant and is planning to keep it.