Do you share a computer? In the history you can right click on the site, choose properties, and you will be able to see the dates that the site was viewed and how many times it was viewed. You would have to take into account how many times you viewed the site and that he could have been on it through his phone as well.
The fact that they are closed though, does it really matter that much to you? If you are happy with your relationship and you don't think he is cheating on you, do you really want to know if he was still looking around in the begining of your relationship?
Forget the checking out of things, the writings on the wall.
open one of your own under a fake name in the same city see what you can find out...
The suggestions here about locating the history created in your computer sound like good ideas. If it were me, I would hire one of those "Rent-a'Geek" people to come over when your husband is not home and find out whatever can be discovered.
Might be better to just share computer time together, and not sweat the ills of the past. I'm sure you have done things you also regret today. If you look, you might find something (irrelevant) that you don't want to find.
You need to go into the profile he has created and more times than not, it will have a "profile created date." Good luck and hope it turns out for the better for you.
That is not evidence, that code only suggest a link from an ad to the site. I think the best thing to do from here is talk to your partner and try to sort it out the good old fashioned way. If your partner gets all defencive or does not want to discuss your genuine concerns, then rethink your position.