It sounds like you're doing more right than wrong I would say.
You and your ex communicate for the sake of the children, there are no longer any big issues between you, and you've gone on with your life.
It is easy to drift back to a place that was familiar, comfortable, and constant. Before all the problems, where there was that hug, somebody steady in your life, a partner to share everything with. I don't think you can be faulted for wanting to feel again, the good things that you felt before, and that all human beings need.
Part of the process of completely moving on is not only living in separate residences and accepting the end of the relationship, but also accepting that with the bad parts over with, so too, are the good parts.
The plus is, what you want, and need, you will find. There is nothing wrong with you for wanting what we all need, and that is companionship. Whether that is a friendship, or relationship, and what each of those consist of, it is natural to want to replace feelings of loss and lonliness to fill that particular void that was lost when you and your wife split.
As you become stronger on your own, there will be less of a shadow following you from the past. When you can meet new people, or women in particular, and be completely free to judge them, and a relationship on its own merit, without comparing to the past, you'll see some headway. One of the reasons that many experts say that it takes a year to get over a marriage, is because after all the dust settles, the emotional adjustment to being independent, takes a lot of time to work through.
At some point, you will feel you are moving forward, without one foot in the past. Such a tremendous loss is much like mouring a death. Even though the person is gone, their 'presence', and the influence they had on your life is still very much alive. But over time, nature allows us to heal from the loss. I don't think you are quite there yet.
You can't make it happen, and decide tomorrow morning that you are completely over your wife, and start a fresh new relationship without still being emotionally tied to her. It's not a fault, and there isn't anything wrong with you. Realizing through the steps of grieving the loss of your marriage, you will come to accept that you are a stronger person, and ready, to invest in a new relationship, without shadows from the past blocking your vision.
Healing, takes time. Take good care of yourself.
