Most Helpful Girl
Girls like to talk about their dating life with their friends. Crushes, problems, the good stuff. I'm sure that isn't news to you. She probably feels more comfortable unloading it on you than her b there friends, because you know that side of her better than they do (seeing as you dated).
I'm staying friends with an ex right now, and currently dating others. I really want to talk to my ex about it because we always used to talk about relationship and sex stuff before, so I'm already comfortable. HOWEVER, even though I want to talk to about that topic, I don't. Because it seems a little disrespectful and taking advantage of the friendship.
A little bit is ok, so you know what's going on each others lives, but not everytime you chat. Just ask "can we talk about something else for a while?" maybe :)