OK Creative now we get to the crux of the matter. So in a nutshell, you cheated on your parter, and he eventually left the relationship..... I am not judging you on what happened in your past - these things happen, but you are right in that having these little 'dreamy' thoughts of 'what could have been' are not healthy for you. And so since this little tape keeps on playing in your head, its no wonder that you haven't been able to move on
. And yes it would be far healthier for you to find a way to move past these thoughts you are currently having.
The thing about emotions is that not many families (or society for that matter) teach their children how to deal with their emotions in a healthy way - as humans, we are designed to feel, however families and society are bent on making us not feel, push it aside, bury it. Does that sound familiar?
Creative, I think that you need to find some self-acceptance in your part in the break up of the relationship. This means that you will have to get in touch with the guilt that you feel over the break up of this relationship. It sounds like you may have pushed the guilt aside and only remember the good stuff. If you are having trouble accepting the guilt, then accept that you are having trouble accepting the guilt. But also accept that one day you will feel differntly.
Once you have accepted the guilt, then you have to work through the emotions, just like you work through any intellectual problem. I can only imagine how I would feel if I were in your position, but I would be castigating myself, I would be furious with myself, but at the same time, I would remind myself that I am only human, and that I can forgive myself, and do better in the future, with my present husband. Feel the feelings for as long as you need to, until a little voice in you says "Right, I don't need to feel this any more". And so you move on.....
A word of caution - Creative, you are quite right that contacting you ex will be of no use to you. That is not what you need in this situation. Remember that accepting and experiencing your feelings does not mean that these emotions have any say in what you do. You can fully experience your emotions and go about your daily business.
While I have only learnt to do this myself recently, I can assure you that I am using this method to move on from some past hurts which have to do with my family and it works. I hope this helps you to find the peace that you are looking for.