Would you go out with a close friends ex boyfriend?

My friend and I are 39.We are close and have been friends since we ae 3.She went out with him when she was 15 for 2 years so that was a long time ago.well fast foward she is married now with 4 kids.I am divorced with 3.he is divorced with 2.we have all gotton together with other friends but she told me he was "off limits"...He has asked me on a date for 2 years and he knows why I wont.I do like him,and we get along great.I told her once i was having dinner with him and 2 others and she wasnt happy and i landed up cancelling out of guilt.I have cancelled with him alone at least 5 times.well thinking about it why should we be apart.she is happily married but doesnt want me with him.Well im going out to dinner tonite with him.I finally didnt cancel.Told him I want to see if there is anything with us alone together.we may feel nothing.Am I wrong?i dont want her to know yet because if i dont have a connection with him tonite then why hurt her but is she being unreasonable not allowing this?