Unsure if this is the right way to behave

I am unsure if this is the right way to behave, so please share your thoughts on this.

I met my best friend in college. She's the person I share everything with, she's been there for all of my mental breakdowns and my depressed episodes. We are part of a group of 7 friends. All 7 of us are really close, but most of us share the deepest stuff only to one or two in the group. (Like a set and subsets, if you will).

Anyway, my best friend S and I are really close. Unfortunately, S isn't always the right person to be with. She does a lot of grey-area stuff (Her parents are super strict. So, she always has a freak-out and does the exact opposite of what her parents tell her, and to hide the mess she made, she blames it on me to her parents). Whenever she's irritated or angry, she takes it out on me, by snapping at me and giving me the silent treatment. I usually apologize even if I'm not in the wrong, as I don't want to lose a good friend. She recently got married and divorced, as the guy she married was a bad person and she had an emotional affair with a guy she loved from college. She ran away from home and the police were involved. Her parents started questioning me, as I'm the only person she's close to.

The rest of my friends do not know the real reason for the divorce. They think that there was some huge fight between them and the families. Meanwhile, her soon-to-be ex-husband started questioning me about the affair. I couldn't take the stress and broke down and told everything to some of my friends from our group, about the affair, about her emotional abuse for the past two years, and the grey-area stuff and how she used to implicate me.

This has created a bad image of her in their eyes. I feel like I'm a bad friend for telling what she has told me, but angry that everytime a problem arises in her life, I'm made the scapegoat and left to deal with the stress alone. Am I justified in sharing what she said to my friends?