What would be your reaction if you caught your boyfriend naked in bed with a lady

My sister's boyfriend used to stay with me and my sister in our apartment. One day we came back from work around 6, and we decided to drop by the apartment to grab a few things before heading out for dinner. I had my keys, so I opened the door, and we could hear moans from my sister's room. I opened the door, and I saw my sister's boyfriend naked in bed with a lady. The lady saw me and my sister, and she had this guilty look on her face. I was enraged; I had never felt so angry before. I had so much adrenaline that I was trembling. I asked my sister to go wait in the car, and then I confronted her boyfriend. He tried to deny it at first, but when he saw that wasn't working, he started begging and crying, saying he was drunk and didn't know what he was doing. I told him to get dressed, and I kicked him out of the apartment. When I got back to the car, my sister was crying, so I hugged her and tried to calm her down. She kept saying it was her fault and that she should have known. I reassured her that it wasn't her fault and that he was the one who messed up. I suggested we go to my parents' house and tell them everything, but she said she needed some time to process it. We went to a park instead, and she cried and vented about the whole situation. I was still fuming and wanted to punch the guy, but I tried to remain calm for my sister's sake. I told her we could file a police report, but she didn't want to. I think she was embarrassed and didn't want to make a big deal out of it. In the end, we just went home, and I made sure she was okay before going to bed.