Oh sweetie... I can understand your being hurt and upset by this. I would be upset and bothered by it as well. What would upset me more is not so much the act (I assume we are talking about pornography here) but the fact that he knew how you felt about it and openly lied to you about it. It's like a secret life, and that is what would bother me the most.
I guess some guys really do have an addiction to these types of things... though I can't understand it myself. It really does NOT have anything to do with you though, but I know I can't convince you of that.
I hope you can work things out with your husband. Try to keep in mind all the good things — like the reason why you fell in love with him in the first place. If he's still that person, then I hope you two can get past this.
