My roommate did his own divorce paperwork in California - you can get a kit that leads you through the paperwork. I think it's more complicated if they contest, but at least it gets the ball rolling. It's probably worth checking with a legal clinic or something like that, regarding what your options are if he does decide to make trouble.
If he makes trouble, however, he will be much less likely to be able to hide that he is still legally married.
I don't think the insurance is too much of an issue, as many plans allow a domestic partner to be added, even if they aren't legally married to you, but you can't add your wife and your mistress to it.