Lunch Surprise Exposed His Double Life

AITA for confronting my boyfriend about his secret life after I found out he was cheating on me with my best friend for over a year? I never thought I would be in this situation. I had been with Mark for three years, and everything seemed perfect. We shared everything, or so I thought. We moved in together six months ago and started talking about marriage. I trusted him completely. One day, I decided to surprise him by dropping by his office unannounced. I wanted to bring his favorite lunch and surprise him at work. When I arrived, I saw him through a window. He was sitting with a woman I did not recognize. They were laughing and holding hands. My heart dropped. I watched as they kissed goodbye and he kissed her cheek before she left. I could not breathe. My mind raced. Who was she? Why was he with her? I immediately called my best friend, Lisa. She had been my confidante for years. I asked her if she knew anything about Mark being with someone else. There was a long pause. She finally admitted that she had been seeing him for over a year. I was stunned. She begged me not to be angry, saying she was sorry and that she loved me. I felt betrayed and sick. That night, I confronted Mark. I told him I knew about his secret life. He denied everything at first. Then I showed him the photos and texts I found on his phone. His face turned pale. He tried to explain that he was lonely and made mistakes. He begged for forgiveness and said he loved me. I was furious. I felt like my world was crashing down. I decided to go to Lisa to confront her. When I saw her, she burst into tears. She admitted she knew about Mark and that she had fallen for him. She said she loved me but could not resist her feelings anymore. I was devastated. I felt like I had lost everyone I trusted. The next morning, I packed my bags and left. I do not know if I should forgive them or if I should cut them out of my life forever. I feel so betrayed and hurt. Was I wrong to confront them so openly? Should I try to salvage this or just walk away? I need advice because I am lost.