The people that are meant to cross paths with you, will. Life is fluid and everyone that we come into contact with presents an opportunity for growth and to learn about ourselves.
That's why trying to chase down a friend or someone to love is not worth it. If that person wants to be around you and you are open to it, the relationship will flourish. If you are the only one putting in any effort, then let it go. Love yourself enough to know that life is just fine without them and figure out what to learn from the encounter, however brief it may be.