I get why you rang the number, catwoman - this creature has affected and hurt you very very deeply, and you want to hurt him back / find out the truth / let him know you know what he is / force him to be a decent human being / have him become a reasonable NRP.
Sadly, you will never be able to get the truth, you can't hurt him (but you can anger him), and decent and reasonable are unlikely to be terms he'll ever be described as.
I can also understand your concerns about his risky behaviour - swinger's clubs, drugs, gay saunas, lies, etc etc. If he's risky with his own well-being and life, who's to say he's not also risky with DS?
BUT.
Which of these things do you want to have happen:
You being bitter towards him from here onwards, that bitterness spills down to DS, DS resents you for not letting him have a relationship with his Dad, he builds Dad up to be some wonderful fantasy figure, meets him and is bitterly disappointed. Meanwhile creature gets to paint you as the bitch who stopped him seeing his DS.
You let it go, let the past go, and look at what is happening now. You let contact resume (in whichever format - see below), and eventually he voluntarily gives up contact as it gets in the way of his lifestyle too much. Then you can always show that you did the right thing, and even if he does take it to court, you can show that you have been reasonable in doing what you can to let him have safe contact with your DS.
If contact has been going well, then it is up to you to help maintain that. Which includes ignoring stuff from the past, but you know that, don't you? If you honestly think his behaviour and life-style is putting DS at risk, then arrange contact at a contact centre - National Association of Children's Contact Centres - you can self-refer for free, usually takes anywhere between a couple of weeks to a few months to get a place, and the sort of contact you're looking at (him and DS in a large room with several other NRP's and DC's with a few volunteers about the place) should be free.