Running alone gives you a lot of time to think. You can experience the full spectrum of human emotion if you give yourself space to actually FEEL. One of the emotions we probably spend the most time trying to figure out, justify, analyze, is love. And most often the thoughts are concentrated on how we are getting love, how we can get more love and why what we already have is not enough.
It's really no different than the way we think about money. To paraphrase my Bishop, Jesus spent more time talking about money than he did about anything else because he knew that people would listen when you're talking about that thing they hold so dear and just can't get enough of. And one thing that Jesus made clear is that in order to get one has to give freely, cheerfully and selflessly.
Is it not the same when you are dealing with the greatest treasure we can offer, that thing we can't get enough of ,but doesn't cost a thing? So it leads one to believe that you get more love when you concentrate less on getting it, and more on giving it. And to get to that point is really an evolution of the mind.
I believe as you truly grow into a loving, caring individual, your thoughts revolve more into what YOU can do better. You spend more time reflecting on your own reaction to situations instead of what the other person should have done differently. And you still think good loving thoughts about those closest to you whether they met your expectations or not. An immature heart says "if you love me you would...." a mature heart says, "it doesn't matter what you do or don't do, I can't help but think fond thoughts of you."