It's pretty pointless to describe it as it would be similar to a spiritual experience. In my case, I really was looking for no one and found it. I've been married to her for 20 years of my life, and I was only 22 when I married. I have absolutely no regrets of that decision. I'm not interested in other women nor even attracted to them at all in that way.
However, there was nothing different from her than many other of my friends (female included) that you could pin that on. There was just something else beyond all of that, something impossible to ignore.
I've had all the other 'love''s before (infatuations, sexual, etc.), none of them compare to that. That true love type of experience is transforming and neither of you can stand to be apart. There was nothing special about our mutual interests even though we had a lot of them, and both had things going on that the other person had no calling to as well. I've changed greatly as a person since that time and so has she. If I merely was using a shopping list of what I thought was important in a relationship nothing on that list would matter now. Neither of us are the same (not even spiritually), we still are together, so it has to be bigger than that to be 'real'. This is probably why divorce rates are so high - people fall in love with criteria rather than the fundamental being of the person. That person will change, and they will break up. Most of the time, when we were dating I just came to be with her - we had no plans at all, and that was just fine. It often took me hours to get to her place, and I'd go rain, snow, or shine. I'd often have to wait 2 hours for a bus service to start in a bad neighborhood - I had no concern at all of myself or what I wanted, she expected me and that meant I was there. Hell or high water.