I am torn

My oldest is 13 and I found out from his father (whom he spends every other weekend with) that over Christmas break he accessed inappriate websites on their computer. I am devestated. I diligently watch and protect my children from these things but I have no control of his fathers lack of supervision. I suggested he password the computer in the future and I got a grown man whining about how other people use it. I couldn't believe it. He seemed more upset about the charges to his credit card and other inconviences than the damage our son has recieved to his innocence. I keep imagining what he saw and it makes me sick. My son and I have not been able to talk about this since I was only told about it Friday and he is still at his father's until Monday night. I am at such a loss as to what I should do. I am angry that it even took 2 months to be told about this. I prayed about it and since I am working on "Biblical Submission" took this to my husband who suggest we speak to our lawyer about ds's father's negligence. I feel like I am so lost at sea on this.

My ds is such a sweet caring child, innocent and comfortable in speaking to both myself and my husband (he has been in ds's life since he was 3) about puberty and sexual topics. So much so that other family found it awkward for our family to be so open. I never thought he would be a child to seek out this, I have a difficult time even believing it. I did ask him before he left about it and let him know how dissapointed we (daddy & me, meaning my hubby) were and he would not meet my eyes. My heart is breaking for this and him because I know how confused he is. At the same time I also know he knows right from wrong, and good from bad. Am I wrong for wanting to protect my child from the degradation his father apparently thinks is OK?