"He probably was [your soul mate]. Your problem is you don't understand what that word means. People think a soul mate is your perfect fit, and that's what everyone wants. But a true soul mate is a mirror, the person who shows you everything that's holding you back, the person who brings you to your own attention so you can change your life. A true soul mate is probably the most important person you'll ever meet, because they tear down your walls and smack you awake. But to live with a soul mate forever? Nah. Too painful. Soul mates, they come into your life just to reveal another layer of yourself to you, and then they leave. And thank God for it. Your problem is, you just can't let this go...[his] purpose was to shake you up, drive you out of that [relationship] that you needed to leave, tear apart your ego a bit, show you your obstacles and addiction, break your heart open so a new light could get in, make you so desperate and out of control that you had to transform your life, then introduce you to your spiritual master and beat it."
It's true. I've always believed that you can only have one "true love" - the person you spend the rest of your life with. Other "loves" are not really loves but actually just lessons and guiders to help you along the path you want to go. They may be important people and they may stay in your life for a long time (even forever) but they are not the person you are supposed to spend your life with - that is reserved for your true love.
This book is very enlightening (when I get around to reading it) and I highly recommend it.