I don't understand why you didn't move heaven and earth and marry him since you weren't married when you met him. Love and interest can only be kept alive by constant thinking about that person, not "letting go" of the relationship (not the Love, never let go of the Love, just the relationship) and moving on. If you can't/don't want to be with him "enough" to do something about it, then not turning your mind to other thoughts until it gets tired of trying to think about him constantly is only hurting you. What you think about is your "choice" in the sense that you can change the "channel" and if you do that often enough, the distance between the need for a channel change will get greater and greater. It's your TV, it can only stay tuned to what you want to watch.