HUH?

Ok. I need some wisdom. Seems I am having a problem. Long of the short is I have a friend who has two ex-girlfriends I am friends with. (With me still?) One girl is a long time friend and one is a new friend. The older friend is under the assumption that I want her and the new friend to be in one place at one time. (Still with me?) This is not an issue because that mistake can happen only once . (Hang on there I am getting to some sort of point.) So some how my older friend is mad because she thinks I am asking her to cross some sort ivisiable line...? (Got it? Great now explain it to me?)