I looked through my brothers (15) computer and found out he sent a dick pic to someone I want to confront him but I feel guilty, advice?

my brother is socially awkward, and has anxiety, and has been bullied most of his life, during this summer he has started talking to other lonely teens like him (using reddit and discord) and to talk to his friends who he doesn't see that much during the summer, one time he left his room with his computer on and I had a gut feeling to check his computer because my parents weren't supervising who he talks to online and I felt like I had to so I did and opened up discord and figured out he has a girlfriend I looked at their most recent conversations and it seemed wholesome except when I scrolled up I was just junpscared by my brothers dick and I closed discord and turned the computer off I want to confront him about sending dick pics to people, but I feel guilty that I looked through his computer without him knowing and in his bio and his girlfriend's bio on discord it seems like they really like each other even though they probably haven't been dating for more than 2-3 months and I don't want to ruin that, and I don't want to ruin the close relationship me and my brother have, advice?