"You know, Justin and I are great friends. We love each other. We want the best things for one another," Cameron Diaz told "Good Morning America" in 2011, long after her relationship with Justin Timberlake had ended and while they were promoting the comedy "Bad Teacher" together.

While the former pair have publicly complimented each other, even since Timberlake has become engaged to Jessica Biel, is being friends with an ex only the stuff of scripts and on-screen romances?

Often when people end a relationship they say, "Let's be friends." It makes sense. You've been the most important people in each other's lives for a long time, maybe even years. It's hard to make that clean break -- it can feel like a gaping hole in your life. So you decide to continue to be a part of each other's life. But staying connected isn't always easy or the best choice. So when, if ever, is it OK to be friends with your ex?

Couples rarely break up on equal footing. Instead, one person might be eager to get away while the other wishes to continue to be together. That's where it gets tricky. If you are on the side of hoping for more with that person, you run the risk of remaining attached and not allowing yourself the possibility of meeting someone new who might be better able to fulfill your needs. And if staying connected was a problem while you were dating, imagine how hard it will be to get your ex's attention now. You may just be setting yourself up for frustration and disappointment which ultimately might make you feel more empty and sad. If you remain focused on your ex, it could hold you back from finding your future.

The rule of thumb, generally, is this: It probably isn't such a good idea to try to be friends unless neither one of you holds any hope to be with the other romantically.

Give it time. And if one of you calls the other after years of no talking? Maybe then there will still be good feelings remaining and enough time and space will pass so the two of you really can be friends.