We had been living together for three years and had what I believed was a solid relationship. He had been working on a business deal that made him work late and night and on part of the weekend. I didn't think anything about it because it had happened before whenever he was up again a deadline. One evening when he was working late, I had dinner with a mutual friend who worked with him. Through a slip of the tongue, I learned he hadn't been working late at the office. I decided to follow him and caught him making out with another woman. He said it was nothing serious. But I felt so betrayed; I just couldn't trust him again. So we broke up.