If there's one thing that leads a relationship down the road to ruin, it's when someone assumes that whatever they do -- no matter how selfish or heartless -- will be forgiven and forgotten, and that his or partner will always be there to receive them with open arms. My girlfriend in high school learned this the hard way. She was as flaky as can be, telling me one minute that she wasn't ready for something serious and reeling me back in the next with hugs and tender messages. Well, she was completely blindsided by my decision to end the relationship only a few months after we began dating. I just couldn't stand the games anymore, and I knew I could do better. I was then on my way to college, where a bountiful crop of single women awaited me. I will admit that I probably asked for it. I was a bit of a pushover in those days, virtually worshiping the ground whichever girl I was interested in walked on. A similar situation played out with another girl I dated a few...