I've been in your situation, as my husband is a recovering sex addict, so I understand how you're feeling, and I'm sorry you have to be asking these questions. My husband also posted and answered ads on Craigslist. Thankfully, he is seeking treatment and has worked very hard to re-establish trust and remain "sober".Please know that there is no fool proof way to prove his activities on the computer. Remember that there are always ways around any limits you try to enforce. There are public computers in libraries, or work computers. There are programs they can use to cover their tracks.It may be impossible to detect the ads he's already posted, unless you set up your own profile on craiglist and respond to each ad to see how each person responds.If you have access to a computer he used, you may be able to view his browsing history, depending on which browser he used. Please let me know what you have access to in terms of his computer, laptop or a smart phone and I can guide you through looking through history.I recommend using a keystroke logging program on his computers and smart phone. This installs a program silently, that cannot be seen unless you perform certain key commands. You would be able to see every keystroke made on that computer, whether in email or on a website. You would be able to log in to see this information on another computer, in real time, or get email alerts when certain words are typed -including Craigslist.If you can start by telling me what kind of devices your husband is using, and what browsers, I can help you begin to establish some feelings of safety and control within your relationship.Please understand his behaviors are part on an illness, not a character flaw, even thought his behavior is unhealthy and considered to be immoral. There is hope if you approach it in this way.
Keeping in mind keystroke logging programs are technically illegal, chances are he may not be using craiglist. There is a new internet phenomenon in casual encounters called OKcupid and Plenty of Fish(acronym POF) where people basically create a profile with a picture, add in some stats and start "fishing". These are incredibly popular and are referenced all across the internet even on random fitness and automotive forums.A friend of mine has a female friend who's boyfriend actually has an addiction to meeting other females on this site and furthering the encounter. He had stopped for a while but recently began using these sites.This will probably take a bit of time, but you could create a ghost account and begin searching within the parameters of what you think you husband might be searching within and find him that way - especially if he is using a public or friends computer.
Just keep in mind - Installing a keylogger on someone else's computer; a computer that does not belong to you (a child's computer is a different story) is illegal. Your own computer is fine, installing it on a smartphone or a computer that belongs to another person is NOT. It violates federal law. I would get in touch with a lawyer asap before doing anything if you fear something will happen within your marriage. The last thing you need is a broken or stretched law to effect the outcome.