How do I tell my parents that my ex of 7 years is willing to leave the country to be with me again?

You are an adult. Your parents will love you no matter what, and you have to make your own decisions! You tell them and be honest about your feelings. They will understand eventually, even if they are upset at first. In the meantime, you will live your life as an adult and show them that you are going to make it even if they have a different opinion.