You say they've been broken up for years (plural), i.e. their lives are separate and distinct now, and yet you feel comfortable confiding intimate facts about her for the sake of alleviating your own guilt?
All of your feelings talk about conflicts with your abstract morals, your interal values, your ideals...
What about the concrete and very real ways in which she is now betrayed? Did you even talk this over with her before you picked up the phone to deal with your own self-involved feelings, blabbing about her personal choices? Maybe she had different feelings than you and thought it was a good thing.
I cannot imagine being more betrayed than having someone expose intimate facts about me to someone who I closed off from that area of my life a long time ago, yet all of your post revolves around your own feelings and only considering the guy who frankly has no business knowing about her sex life if she doesn't want him to know.