OK. I may get in trouble for this but I think it's a testosterone (t) problem. Biologically, t has a very strong control over a humans behavior. Even women have spurts of t , and some have more t and therefore more uncontrollable sexual desires that play out into activities due to the t drive.

I've worked with men who had uncontrollable sexually fantasies about children or rape and they chose to be chemically castrated with female hormone shots of depo provera to lower their testosterone to below a woman's. They said it worked. They said the fantasies stopped. 

Of course this is an extreme example, but put it into your husband's perspective, he's got an overactive imagination, which can be good if channeled in the right direction, but with surges of testosterone he's going over the edge of your (and most women's) views of what's acceptable because he has a strong urge to act out these sexual fantasies.

It's very interesting to follow through with this hypothesis. Unfortunately for some, even if the testicles are removed (chemically or physically) enough testosterone can be generated from the male body to follow through on perverted fantasies. One man was arrested for molesting dozens of kids after he was castrated. 

I still think so many of the worlds problems (PMS, adolescence, sexual crimes, wars) could be cured if we figured out hormones, but not much has changed in 50 years.

 He could get his testosterone level checked and if it's too high they may give him something to lower it because docs understand the psychological damage and it may cause physical problems too. 

It's easier to address the problem if he's not on t overdrive. Then you can talk about the relationship and different things.

I agree that you need to ditch this idiot.  Subjecting a partner to risky sexual activities is a screaming symptom of abuse and objectification.  RUN, don't walk.  Post back on how you're faring.