Abandoned Again

Everyone keeps saying that people will come and go in my life. "People are here for a time, a season, or a reason," one lady said. Maybe words like that help other people, but not me. Other people don't have a life riddled with never-ending abandonment. I can't even adequately describe the abandonment I've faced over and over. You would think it would get easier, but it doesn't. On the contrary, it seems to get harder. I find people who make promises and prove their trustworthiness, only to leave me. It would be one thing if they were in my life for a while and they left me. But it seems that just as I get close and comfortable with someone they leave. My close friendships never last longer than 18 months. Why? What's wrong with me?