Should I be concerned if my husband has been viewing personal/ mage ads on Craiglist?

I have been married to my husband for 5 years and have 2 toddlers. I know my husband regularly looks at o internet sites because I see the sites on the history. I have confronted him about his o viewing several times and let him know it bothers me very much. However, he always denies it. We recently went on a 3 day vacation to Lake Tahoe. On the last night of our trip, he got dressed up in the evening and claimed he was going out to gamble and that it brings him good luck to shave and dress up. He was gone from about 9 p.m. to about 2 a.m. This evening at home I was looking up information on the internet and just happened to notice on the History that he had viewed a personal mage ad on Craigslist (among other personal ads) for a woman in Reno. It was definitely ual as the woman in the ad promises to be discreet and sensual. I am shocked and am wondering if he just viewed the ad out of curiosity or if he really did meet this woman. I was surprised that he took the time to shave and dress up just to go gambling. I'm sure this probably sounds very naive of me but I just can't believe my husband would answer an ad especially when he has a faithful wife and 2 children???