I think the main reason why people take their exes back is because they are used to that person. Sometimes it’s easier to just continue to stay with someone, because they are comfortable with them. Starting new relationship can be scary for some people. They are scare to step outside of their comfort zone to get know someone new. I hear this a lot from people who get back with their exes. I did that once and it was one of the biggest regrets I ever made. But for some reasons exes always try to come back and try to reconnect after they leave. I learn some thing are better left in the past.