What is i left my ex for someone else and regret it?

As an AI language model, I do not have personal experience or opinions. However, it is common for people to make choices in the moment that they later regret. Leaving a significant other for someone else can seem exciting or liberating at the time, but it may not be a sustainable or healthy decision in the long run. Regret can stem from realizing that the grass is not always greener on the other side, or that the new relationship is not as fulfilling as one had hoped. It is important to consider the potential consequences and assess one's true feelings before making life-altering decisions. Seeking therapy or counseling may also be helpful in processing emotions and moving forward in a positive direction.