I am super ashamed of myself for what I did to my girlfriend. It's been almost one year and a half of relationship. But I was dishonest with her. I had a major crush on her sister, and I was assuming that I would deal with these emotions and get back to my girl. I failed at the end, and I was quite wrong. Not only I couldn't ever forget her sister, but also I lost my feelings toward my girlfriend. After 2 weeks of fighting and breaking up, which was like hell, I am super fucked up and I have no choice except searching, reading, talking to get a little better.
What should I do?