Why can't I let go of past relationships? Sometimes I still catch myself thinking about my exes.

Whenever you are in a committed and loving relationship you give away a little piece of your heart. So when you and the person breakup they still have that part of you and you have a part of them. There will always be a connection with that person. However, the important thing is not focusing on letting go, its moving on. When you move on you accept the fact that that relationship did happen and that it ended for a reason. Also, when you find that right person all the pieces that you gave away will suddenly not matter because you will be whole. The way that I like to think about it, is that everyone gives away pieces of themselves to people. When you find that person that you are meant to be with the pieces of you and the pieces of them fit together to make you both whole.