O.K. Here's a good one. Why would my husband lie to me when he knows I knew what happened??!!

My daughter called me at work the other day to tell me something but she didn't want to tell me because she knew I woukd get upset if she told me. I had no idea what it was. I thought she broke the laptop or sonething. She had walked into the den where my husband had his computer on and a dating site up on the screen. He was in the other part of the house and did not know she had gone in there to get something and she saw it and called me to tell me about it. That evening I asked him why he was on it and he denied it first and said he was just looking for someone he knew. I don't do this and don't understand why he has to do this. I have very little trust and respect in him now. Our anniversary is next week and I don't know what to do.