Well, for me, it's not.
Once you befriend your ex, it means you still have those crazy feelings over him/her.
[b]Unless you still want him/her in your life.[/b]
[i]Any comments?[/i]
Befriending your ex doesn't actually mean you still have those feelings you once had for him. I don't see anything wrong with befriending your ex, as long as you consider other people's (your girlfriend/boyfriend, his/her girlfriend/boyfriend) feelings. Everything is okay as long as you know your place/limitation in the situation.