Nasty situation for you to be in - others have given some great advice and viewpoints. I hope you don't mind if I add mine...
As you have said, it's up to each of you to choose which relationships you are in and how to nurture them. But I think it's also important of you to communicate anything that you see that is problematic so that he can take it on board. If that has been communicated clearly (and it sounds like it was) then it his up to him what he does with that information.
A lot of folks (me included) get blinded by NRE - this is why I tend to trust the instincts of my partners and why I like it if they meet any new prospective folks that come into my life.
If you try to influence too much, he will end up resenting you and possibly blaming any failure of the relationship on you. He has to get there himself. It can be painful to watch, I know.
You also need to protect yourself, though - this may be setting some boundaries for activity - like sleeping in your bed, or the fluid bond that you have with your husband (if she is habitually lying about her relationships, how can you trust her safer sex practices?).
Try to document what you have discussed with him. When this episode passes, in the calm after the inevitable storm that is coming, sit him down and talk about how something like this can be avoided in future. Without getting into "I told you so" mode, note that you saw a lot of problematic behaviour that made you uncomfortable and he seemed oblivious to.
This will help him to develop his own spidey-sense when it comes to future relationship material.
"Listen, or your tongue will make you deaf." - Native American Proverb