Secrets in a marriage are never good. No matter how innocent you think they are, your spouse does not feel the same.
I remember while going through my divorce, I was dragged out to dinner with my sister and her husband (at this point I pretty much wanted to crawl in a hole and die, so I had to be dragged everywhere). As we sat at the table, I across from my sister and her husband, who sat next to her, I witnessed something so foreign to me. My brother-in-law opened his phone (yep, it was a flip phone that he kept until like a year ago) read a text, laughed, responded to the text and then held it over for my sister to read. She read it, they exchanged a few words and that was the end. As I sat dumbfounded, my expression must have shown my bewilderment, my sister asked what was wrong, was I okay? I asked her if her husband did that a lot. Of course, she was lost and confused. I asked her did he often show her texts on his phone? Now she was totally confused as to why would I ask such a question.