In a perfect world, yes. However, unfortunately, this will only bring unnecessary drama to your life. Unless you are like me, a good friend is a good friend. An ex is an ex. Only you know these people so I can only offer my suggestion. Do what you feel is right for you and your ex's ex girlfriend.
i am friends with my husband's ex-wife. did the ex do anything to you? is there a reason why you should not like her besides being your boyfriends ex? whatever happened between boyfriend an ex is their business, is in the past, and has nothing to do with you. be friends with the ex if you want.
You can if u wanted 2 but its probably not a good idea. What would happen is if she ended up in another relationship so many things can happen. For example..... You could end up getting really jealous. and jealousy can ruin relationships easily.