I have never quite understood remaining friends with ex-significant others. It seems insulting to say to someone "you are good enough to be friends, but not a permanent lover." If being taken as a permanent lover is most personal form of acceptance, it stands to reason that being spurned as a permanent lover is the most personal form of rejection.
For you married folks, the presence of a former significant other means that a spouse must live in the shadow of someone who might have been 'the one' in different circumstances. It is not fair to the spouse. One of our responsibilities when we marry to make sure that our spouses know not only that they are the platinum standard of intimate relationships, but also that they are the only standard of intimate relationships.
And the title of this entry...it is from "In My Life," by the Beatles, although it has been covered by Judy Collins and by Bette Midler, among others. Like many things, I have come to appreciate that song more and more as I get a little older. The memories of relationships past are part of who we are. That is okay. "But these memories (should) lose their meanings, when I (we) think of love as something new."
Have a good evening all.