Is AUTHOR wrong in the post ? POST : This is my first post ever so please forgive me if I've made any errors in formatting.
There are 4 people involved in this story (fake names for privacy obviously)

Me
Harry (My best friend)
Abigail (Harry's girlfriend) 
Austin (the person Abigail hooks up with)

This happened around 9-10 months ago, at this point  everything was going well their relationship was going on well (had a few bumps just like other relationships) but around a month before shit hits the ceiling Harry was always suspicious of Austin and even though Abigail knew about this she used to joke with Harry about if they had a fight she would go to Austin for comfort and all that. Oh and I had Abigail's Instagram account cuz she followed like 20-30 meme pages and I cba to follow those many so she happily gave me her account.
Now one random day I was scrolling through those pages and getting my daily dose of memes like any other day but on this day I saw a text notification that caught my eye, normally I ignore those and concentrate on my memes but this one was quite confusing. It was a text from Austin saying " I don't wanna talk to you rn, no I'm not leaving you I just don't wanna talk right now". Now those confused the hell out of me considering she was dating my best friend and from what I knew they were still together. (This is a very gray area as in the aftermath of this whole situation Abigail was saying they were on a break while Harry was saying they weren't very Ross Rachel like)  I take a screenshot of those texts just in case and move on. I thought maybe I misunderstood the situation or something but then the following chat they had confirmed my suspicions
Austin: It felt amazing so calm down
Abigail:Thanksss, sometimes just to piss Harry off I used to rub his dick under the table in tuitions like how I rubbed you yesterday
Now when I read that I was like what the actual fuck so I ended up waiting for more evidence and got it then took screenshots and sent it to Harry which resulted in so much shit which still goes today.
Ever since I've always wondered whether I did the right thing or not cuz this whole situation definitely fucked up Harry's head.
If there's any confusion I'll try my best to clear it up in the comments 