AITA for exposing my cheating boyfriend and best friend?

AITA for exposing my boyfriend after I found out he was cheating on me with my best friend? I never thought I would be in a situation where I would have to confront betrayal from both my partner and m...

AITA for exposing my boyfriend after I found out he was cheating on me with my best friend? I never thought I would be in a situation where I would have to confront betrayal from both my partner and my closest friend. It all started two months ago when I noticed my boyfriend, Mark, acting strangely. He was secretive about his phone and would often hide it when I entered the room. I brushed it off at first, thinking I was overthinking. But then I started noticing little inconsistencies. He was missing from work at odd hours, and I would find unfamiliar lipstick marks on his collar. One night, I decided to follow him. I waited outside his apartment and saw him enter with someone I did not recognize. My heart sank. I decided to sneak closer and peek through the window. To my shock, I saw Mark kissing my best friend, Lisa. My world collapsed. I felt like I had been punched in the stomach. I could not believe it. I needed proof, so I took pictures from outside. The next day, I confronted Mark. He lied at first, denying everything. But I showed him the pictures. He froze. I told him I was done. I also decided to confront Lisa. I thought I should hear her side. When I called her, she adm...