You are still in the throes of the upheaval of the affair. As time goes by, and your relationship goes back to normal, the insecurity will fade. I understand being haunted by the idea that your husband preferred to be with someone else. That happened to me when my husband had an affair 1 1/2 years ago. When I look back at the things I wrote then, they surprise me. I no longer even remember feeling so insecure. But the thoughts of him with her did haunt me. They went away with time and reassurance from him.
Some of the best advice I got at the time, when we were doing our Retrouvaille weekend, was to tell the truth, but no one says what depth of truth to go to. I found a shallow depth to be quite enough. If you leave the past behind, what difference does it make what went on then?