I'm currently writing Chapter 7 Dead End Relationships. Part of making the next or current relationship work is knowing why the last relationship failed. Oftentimes there is a major difference in opinion or expectation that made itself known long after the relationship got serious. Maybe the other person said or did something that was unforgivable. Or maybe the other person lacked certain relationship skills.
Of course, be honest with yourself – it may have been something you did as well.
Bottom line, learn from your mistakes so you don't waste your time repeating them. (And hash out as many issues as you can before getting too serious.)
Good luck, and stay hopeful!