Does every relationship you get in fail? Do you need answers? Most failed relationships start with lack of communication! You have to open up to one another, so that you can lay out all of the issues.
Your partner can not read your mind. Communicate, so that you are both on the same page. Trust is also a Key Word! When you experience chemistry with a person, it does not mean they are fit for you.
You have to want the same things out of life. Understand one another. People can sometimes change in time an decide it isn't the life they want. That would not be your fault, Simply theirs!