Disturbing things discovered

I had previously posted a question here about wether or not I should give my marraige a second chance.  I was seriously considering it.  Then I happend to start nosing around in my computer (which my husband had in his posession for at least 10 days after I left him).  I found out that the morning of the day I left, when he was supposedly devastated about loosing his wife and being able to see his son every day, he signed up on a sex/swinger dating website and immediately began talking to women looking for sex and whatever else.  He stopped making our house payments and now the home we owned is in foreclosure, but he apparently had/has the money to pay 29.95 a month for his sex/swinger website membership...a Gold Membership none the less.  He was even talking to strange women on this site about our son and about how he is trying to teach our son about "values".  I was livid, especially since he brought talk of our son into the perverted world of online sex.  I also went back to our home, without him knowing, and found pornography, and I mean PERVERSE pornography involving animals, pregnant women, hermaphrodites, etc.  I also found some "normal" pornographic materials, pictures and DVD's out and in plain sight and reach of our son.  I was at a loss for thoughts and words at that point.  I asked myself, "Do I even know this person I married?"  We hadn't even filed for divorce yet when he signed up on this website.  Could the information I have on my computer be used to my advantage.  He is trying to fight me for joint physical custody of our son.  Please, any advise??