I just found out my husband is signed up with dating sites. How can I find out which?

I have been married for three months now and am eight months pregnant with my and my husband's first child, a daughter. Recently, I discovered in my husband's email (I had a legit reason for being in it and he agrees) that he had received a message from a dating site. Apparently, he had an account and profile on this site and in his favorites list were three women that apparently live locally. I showed it to him and he swore he had never seen it and he deleted the account immediately. Later that week, (admittedly snooping), I looked at his other email inbox that he only uses for work. It had an email in it from a Group that he was a member of that was for Strip Poker (pretty much a site for playing strip poker via webcam and or chatting with singles). He again erased it in front of me and apologized. He swore he didn't add himself to that group and when we checked his settings it appeared that he could be signed up automatically to some groups without his permission. So I chose to believe he was being honest and he changed that setting so it wouldn't happen again. Then, back on his personal email I found a strange address in his contacts. I checked out the site it had come from and it was a dating site for married men looking to cheat. When I went to the site, his username and pword were pre-entered. So, it appeared he'd been to this site from our computer before and the comp stored the info. If this is true, it had to happen recently, since he's only been married to me these last 3 months. Obviously, I was devastated, but he swore he had never seen that site and erased his account. Now, just yesterday, he received an email from some chick who thinks she's his "soul mate" based on what she read about him on "the dating site". The site wasn't named in the email, but apparently he has personal info and his email listed on there. He wrote her back saying he was happily married and asking what site he's listed on, but there hasn't been a response. I want to resolve this situation before our daughter is born. I want us to be focusing on her, not marriage crises at that time. If there is any way I can find out what sites he may be on, please tell me. I just want it to be dealt with and put behind us. He swears it isn't him signing up to these.Hopefully, he's telling the truth, and if not he isn't going to fess up any time soon. So I just want to find out for myself and try and resolve it that way. Please help with any advice you can offer. Thanks so much...... And please realize that my husband is not a bad guy. It sounds crazy to take his word on so many "coincidences", but i you knew him, you'd understand. I don't know for sure that I can trust him and that hurts... but I very much want to.