If you think on it, how many people have come into your life and wanted to stay? There are so many people we will meet in our lifetime and most of them will go.
Sometimes it's because that's just how it goes — life changes. Other times it'll be because someone's ego gets in the way of your friendship. And sometimes it'll be because no matter how much we loved them, they weren't good to us.
The people that are meant for you, that care about you, will try to show it. They'll always be around and they'll always come back. The ones that aren't will leave, and it's fine to let them go. Remember them in the way that makes the most loving sense.