Just found out

Ok confusing story. Ive been with my bf for 3.5 years. We were engaged but i ended it before i found out about him cheating. It was with a friend of ours over 7 months ago. He says it meant nothing and made him feel horrible. But i knew before i knew about them commiting the act that they were talking to eachother about getting together. He does not want to give me details about what happend. Ive done my best to forget about his actions but i still find myself having a broken heart.