I fucked my best friend while she was engaged [MF]

Kat, one of my closest friends of almost 15 years told me she was engaged to this guy she had been seeing for about a year. He lived in another country, so I still hadn’t met him, but they had seen each other many times and seemed to be really happy. We had seen each other in good and bad relationships and it was nice to think she was finally getting some peace and love. I would tell her how excited I was to know him and how I hoped we would all be friends. Turns out that after this story, we found out he was cheating the entire time so she dodged a bullet.