Why boys don't like good girls?

Sarah

I've cried so much today that my heart can't take it anymore. I understand when someone break up with you because you cheated or did something bad to them. Today my boyfriend broke up with me for no reason. I've never cheated on him,never disrespect him. I didn't expect that from him. My heart is broken. The reason why he broke up with me is that couples of months he cheated on him and one of his friends told me and he admitted so he asked me how I found out about it but I didn't want to tell that his friend told me because I promised to his friend that I won't tell him so he became mad and broke up with me. I feel really stupid because I forgave him after he cheated. I know I am a good person and never done anything bad to him so I don't know why he's doing this to me.