It's ridiculous to say that if you love someone you should let them go and, if they come back to you they are yours forever or if they don't then it was never meant to be.
If you truly love someone never let them go. Your biggest fear would be to lose them. If you love someone you must battle each day to tolerate differences and communicate each others virtues.
Saying it was never meant to be is an excuse to say you couldn't resolve your problems.
Love unconditionally, kindly, but above all moderatly.