Some people feel that once someone leaves your life they will never come back. They feel that if you miss your chance with someone or it does not work out, than it will never work out. That is not always true. Sometimes it is all about timing.
There are people in this world who have reunited with their loved one 20 years later. Life made them go in separate directions but then somehow fate brought them back together. When they reunited they got their happily ever after and couldn't be more happy with each other.
If a relationship is meant to work out it will. If you are meant to be with someone you will be with that person. It may not be the time you want it, but at the right time the both of you will be together. So don't worry how things look like now.
Don't listen to people who tell you different. If you get a vibe that someone will come back into your life, that person just might. When people met when they are young sometimes one of those two people is immature. Years later they grew up. People do change and second chances do exist. After all if something is meant to be it will happen no matter what.