This is tough question, if she is your friend and you respect her you would not go out with her ex bf though if you have got strong feelings for him and he still hasa strong feelings for you and you really want to get together with him then speak to your friend tell her how you feel. Yes it will probably be awkward at first but if you have a chance for an amazing relationship with this guy is it not worth it? that is the morally right thing to do if you really like him. The could go behind her back and go out with him… but if your relationship got more serious she would eventually find out about you and her ex and would hate you for not telling her and going behind her back and you would lose a friend. Friends are very important they always stick by you whereas bf come and go so if she is a true good friend to you maybe you should give her ex a miss, ther’s plenty more fish in the sea. Though if you think about how you became good friends with his gf… was it so you could get closer to her ex bf? because that would show that she is not really a true friend.
Personally I would always get the all clear from a friend before I could date their ex-bf as most girls still feel it’s their property. So if you really value her as a friend and see yourself and her ex having a good relationship, go for it!
Hope this helps 🙂
js1585