Not sure about the codependent thing but I know that when I post here it isn't helping with that whole 'detaching' thing so I try to remind myself to not get sucked in or not read every single post.
It would be nice to think that someone's story is going to be in an indicator of how someone else's would turn out but to me that is an oversimplification of a complex issue. It may or may not. So many other variables in place that the a post does not reveal.
In addition to triggers, there is a lot of projection that goes on (which happens when you are dealing with very personal and emotional issues). We see ourselves (or think we do) and try fix the mistakes we made through someone elses story.
Were it that easy...