I [24F] told my brother-in-law [28M] that my sister [27F] cheated on him and now my entire family has turned on me and I need help

I don't want to give too many details here because the entire world can see this but in summary my sister recently got married to her boyfriend of five years. I'm a little distant from my family and live in another state where I went to school but I've always thought they were mostly good people I could trust.
Three weeks ago when I was visiting my parents along with my sister and her husband, my sister privately mentioned to me she had cheated on him a few years ago but was "so glad things had worked out." She just kind of blurted it out to me in a weird way and I think she regretted saying it herself, but I was shocked and pressed her for details. She then admitted he never knew but she "ended the affair" and was a better person now. Over the next week her story shifted to it being a "one time fling" instead of an "affair" and that she had told her boyfriend (now husband) and they reconciled. Now she's apparently claiming it never happened and I'm completely lying.
When she first told me, I was shocked and didn't really know much what to say except I told her she really should tell him because it's not right to basically continue a relationship with someone like that under false pretenses and I mentioned how she knows my relationship with my boyfriend had ended recently because I found out he was cheating on me. She disagreed and said it was different because there was no point in bringing up something from so long ago when she had matured and changed so much. Then she said she shouldn't have told me and made me promise not to tell anyone else because I had no right to ruin her marriage over it.
Over the next few days I tried approaching her about it alone but I'm not good at confrontation and she got more and more defensive and eventually started avoiding me. She also started to claim she had already told him and stuff like that. There was no way I could talk to her husband alone since she was with him all the time.
After I left I tried calling my sister to talk to her more on the phone about it but she yelled at me and told me not to call again or she'd block my number. After that I didn't do anything for over a week but the guilt was eating away at me, especially since I know what it's like to be cheated on since my own boyfriend of three years did that to me. I thought about talking to my parents but I felt like her husband (my brother-in-law) deserved to be the first to know before everyone else but him found out and had a chance to gossip about it. I truly thought they'd obviously agree with me anyway so there was no point.
So last week I called my brother-in-law and told him everything I knew. He asked a few questions and thanked me but got really quiet. Then a few days later I got a call from my mom who was really angry and asked me what the hell I was doing trying to ruin my sister's marriage. I told her my perspective and that I was just letting her husband know something he deserved to be aware of. She told me my sister had told her something different than what I told her but that either way it wasn't any of my business and I should stay out of it. Eventually she even dared to bring up what happened with my ex-boyfriend and insinuate I was somehow doing this because I was jealous of my sister or projecting or something. Yeah... I'm projecting because my boyfriend cheated on me like my sister did to her boyfriend and I know how it feels and think he deserves to know. I lost it after that and told my mother I never wanted to talk to her again. She called back later and I did answer but her views haven't changed. She apologized for bringing up my ex-boyfriend and claims to be unsure whether to believe me or my sister's version of events, but most importantly she claims it doesn't matter who's telling the truth because "either way" it wasn't any of my business and I shouldn't have butted in. How could someone think that? I feel like I don't even know my own mother anymore.
I haven't called my dad but he hasn't reached out to me either so I guess he's siding with my mom and they've all basically sided with my sister who by the way lives close by them. Then yesterday I found out my brother-in-law blocked my number and I have no idea why. Did my sister actually convince him I was lying? Now I regret not telling him in person but there was no way I could do that at the time. I'm not very clear on what exactly the situation between my sister and brother-in-law is at the moment but he must have at least brought it up to her.
I just feel so alone now and there's no one I can talk to about any of this. I feel like all of my closest family have just betrayed me and shown they weren't the people I thought they were at all. It makes me very sad and depressed and I can't barely even eat lately :/
TL;DR I told my brother-in-law my sister cheated on him a few years ago and now my parents are blaming me for butting into their marriage and everyone seems to be abandoning me. I'm really depressed and I don't understand how this could happen or if I'm somehow the crazy one. Any advice appreciated.


Source.

That was not your place. You're a shlt stirrer.