I would like to interject if I may, as I have had this experience hit me squarely in the jaw. As Will stated, as long as she will not try to sabotage your relationship with him.
My ex-wife absolutely tried to ruin my relationship with my ex-girlfriend by attacking my character. My ex-wife talked of me very negatively and I was quite upset with my ex-girlfriend for taking this trip down memory lane with her.
I informed her the nature of our split when we first met and stated that my ex-wife was very manipulative and bitter because she knew she gave up a good man because she cheated in our marriage. This was a clear opportunity for my ex-wife to damage my new relationship and it created some animosity in me concerning trust issues with my ex-girlfriend. So much in fact, that I broke up with her because of this.
She knew my character based on my relationship with mutual friends, the community, my children and my church but couldn't believe how badly my ex-wife had treated me and confronted her on various topics concerning me. Some of these topics included my finances, demeanor and career status. She later found out that my ex-wife was a truly, horrible person by fate but it left a bad taste in my mouth.
The ex-girlfriend is on the bubble with me and she realizes that it has affected our relationship severely.
Be careful but honestly, I would take what she says with a grain of salt. Honestly, would you want to talk to an ex-anything concerning your boyfriend? Your relationship with him should be your business, not hers. And if she is very positive about him, why aren't they still together?
I would be more concerned about a lingering friendship with an ex then a non-social relationship with an ex any day.
Just my thoughts!