I can only help you from a therapist's point of view. ED and medications for ED is best addressed by a doctor.
It seems that he has become sexually addicted to this fantasy and this is causing him to constantly bring this to you. When someone becomes obsessed with a fantasy the other person's needs are not considered. It is all about fulfilling this fantasy. He is the only one who knows where this originated or why. There may not even be a reason. Sexuality is a very personal part of our personality. He seems to be obsessed with having high risk sex either you or the both of you. You have to stick by your guns because anything that you agree to do will be along these lines.
Porn and other vehicles is less intrusive than involving you with other partners. The best resolution to this issue is to have him see a sex therapist. He has to of course want to learn why this is so important. The next best solution is to involve a couples counselor to see you both. He has to realize that this is hindering your relationship. This is a complex issue that has to be explored over time. A therapist can explore the issue of sexual addiction.
This obsession may have been born of his previous marriage but he has to be willing to resolve this now to be fair to you
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