The time. All of that time. All of that time that you spent with the person who you thought would never ever leave you, only to find out that it was going to end just a little bit down the road. That they were going to leave your life. In some cases they may stick around because they still care about you. But in a lot of cases that doesn't really happen. When they leave you probably won't see them ever again. No one really wants to be reminded of the pain or the past or even what could've been. Thinking about that would just make anyone extremely sad. Sometimes though remaining friends is kind of a nice thing. Yes, you have history together but that doesn't mean that in time you can't become friends. It probably won't be the same but that's what happens.